SyntaxError with WMT datasets
Hi @patrickvonplaten!

I'm now getting the below error:

```
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-28-3206959998b9> in <module>
      1 import nlp
      2 
----> 3 dataset = nlp.load_dataset('wmt14')
      4 print(dataset['train'][0])

~/.local/lib/python3.6/site-packages/nlp/load.py in load_dataset(path, name, version, data_dir, data_files, split, cache_dir, download_config, download_mode, ignore_verifications, save_infos, **config_kwargs)
    507     # Instantiate the dataset builder
    508     builder_instance = builder_cls(
--> 509         cache_dir=cache_dir, name=name, version=version, data_dir=data_dir, data_files=data_files, **config_kwargs,
    510     )
    511 

TypeError: Can't instantiate abstract class Wmt with abstract methods _subsets
```


The following snippet produces a syntax error:

```
import nlp

dataset = nlp.load_dataset('wmt14')
print(dataset['train'][0])
```

```
Traceback (most recent call last):

  File "/home/tom/.local/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 3326, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)

  File "<ipython-input-8-3206959998b9>", line 3, in <module>
    dataset = nlp.load_dataset('wmt14')

  File "/home/tom/.local/lib/python3.6/site-packages/nlp/load.py", line 505, in load_dataset
    builder_cls = import_main_class(module_path, dataset=True)

  File "/home/tom/.local/lib/python3.6/site-packages/nlp/load.py", line 56, in import_main_class
    module = importlib.import_module(module_path)

  File "/usr/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)

  File "<frozen importlib._bootstrap>", line 994, in _gcd_import

  File "<frozen importlib._bootstrap>", line 971, in _find_and_load

  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked

  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked

  File "<frozen importlib._bootstrap_external>", line 678, in exec_module

  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed

  File "/home/tom/.local/lib/python3.6/site-packages/nlp/datasets/wmt14/c258d646f4f5870b0245f783b7aa0af85c7117e06aacf1e0340bd81935094de2/wmt14.py", line 21, in <module>
    from .wmt_utils import Wmt, WmtConfig

  File "/home/tom/.local/lib/python3.6/site-packages/nlp/datasets/wmt14/c258d646f4f5870b0245f783b7aa0af85c7117e06aacf1e0340bd81935094de2/wmt_utils.py", line 659
    <<<<<<< HEAD
     ^
SyntaxError: invalid syntax
```

Python version:
`3.6.9 (default, Apr 18 2020, 01:56:04)  [GCC 8.4.0]`
Running on Ubuntu 18.04, via a Jupyter notebook
SyntaxError with WMT datasets 
 The following snippet produces a syntax error:

```
import nlp

dataset = nlp.load_dataset('wmt14')
print(dataset['train'][0])
```

```
Traceback (most recent call last):

  File "/home/tom/.local/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 3326, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)

  File "<ipython-input-8-3206959998b9>", line 3, in <module>
    dataset = nlp.load_dataset('wmt14')

  File "/home/tom/.local/lib/python3.6/site-packages/nlp/load.py", line 505, in load_dataset
    builder_cls = import_main_class(module_path, dataset=True)

  File "/home/tom/.local/lib/python3.6/site-packages/nlp/load.py", line 56, in import_main_class
    module = importlib.import_module(module_path)

  File "/usr/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)

  File "<frozen importlib._bootstrap>", line 994, in _gcd_import

  File "<frozen importlib._bootstrap>", line 971, in _find_and_load

  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked

  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked

  File "<frozen importlib._bootstrap_external>", line 678, in exec_module

  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed

  File "/home/tom/.local/lib/python3.6/site-packages/nlp/datasets/wmt14/c258d646f4f5870b0245f783b7aa0af85c7117e06aacf1e0340bd81935094de2/wmt14.py", line 21, in <module>
    from .wmt_utils import Wmt, WmtConfig

  File "/home/tom/.local/lib/python3.6/site-packages/nlp/datasets/wmt14/c258d646f4f5870b0245f783b7aa0af85c7117e06aacf1e0340bd81935094de2/wmt_utils.py", line 659
    <<<<<<< HEAD
     ^
SyntaxError: invalid syntax
```

Python version:
`3.6.9 (default, Apr 18 2020, 01:56:04)  [GCC 8.4.0]`
Running on Ubuntu 18.04, via a Jupyter notebook 
 Hi @patrickvonplaten!

I'm now getting the below error:

```
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-28-3206959998b9> in <module>
      1 import nlp
      2 
----> 3 dataset = nlp.load_dataset('wmt14')
      4 print(dataset['train'][0])

~/.local/lib/python3.6/site-packages/nlp/load.py in load_dataset(path, name, version, data_dir, data_files, split, cache_dir, download_config, download_mode, ignore_verifications, save_infos, **config_kwargs)
    507     # Instantiate the dataset builder
    508     builder_instance = builder_cls(
--> 509         cache_dir=cache_dir, name=name, version=version, data_dir=data_dir, data_files=data_files, **config_kwargs,
    510     )
    511 

TypeError: Can't instantiate abstract class Wmt with abstract methods _subsets
```

