LocalDatasetModuleFactoryWithoutScript extracts invalid builder name
Ok, so
```
os.path.basename("/home/user/")
```
gives `''` while 
```
os.path.basename("/home/user")
```
gives `user`. 
The code should check if the last char is a slash.
 The fix is:
```
"name": os.path.basename(self.path[:-1] if self.path[-1] == "/" else self.path)
```
## Describe the bug
Trying to load a local dataset raises an error indicating that the config builder has to have a name.
No error should be reported, since the call is completly valid.

## Steps to reproduce the bug
```python
load_dataset("./data/some-dataset/", name="some-name")
```

## Expected results
The dataset should be loaded.

## Actual results
```
Traceback (most recent call last):
  File "train_lquad.py", line 19, in <module>
    load(tokenize_target_function, tokenize_target_function, {}, tokenizer)
  File "train_lquad.py", line 14, in load
    dataset = load_dataset("./data/lquad/", name="lquad")
  File "/net/pr2/scratch/people/plgapohl/python-3.8.6/lib/python3.8/site-packages/datasets/load.py", line 1708, in load_dataset                                                                           
    builder_instance = load_dataset_builder(
  File "/net/pr2/scratch/people/plgapohl/python-3.8.6/lib/python3.8/site-packages/datasets/load.py", line 1560, in load_dataset_builder                                                                   
    builder_instance: DatasetBuilder = builder_cls(
  File "/net/pr2/scratch/people/plgapohl/python-3.8.6/lib/python3.8/site-packages/datasets/builder.py", line 269, in __init__                                                                             
    self.config, self.config_id = self._create_builder_config(
  File "/net/pr2/scratch/people/plgapohl/python-3.8.6/lib/python3.8/site-packages/datasets/builder.py", line 403, in _create_builder_config                                                               
    raise ValueError(f"BuilderConfig must have a name, got {builder_config.name}")
ValueError: BuilderConfig must have a name, got
```

## Environment info
- `datasets` version: 2.2.2
- Platform: Linux-4.18.0-348.20.1.el8_5.x86_64-x86_64-with-glibc2.2.5
- Python version: 3.8.6
- PyArrow version: 8.0.0
- Pandas version: 1.4.2

The error is probably in line 795 in load.py:

```
 builder_kwargs = {                        
     "hash": hash,
     "data_files": data_files,
     "name": os.path.basename(self.path),
     "base_path": self.path,
     **builder_kwargs,
 }
```

`os.path.basename` for a directory returns an empty string, rather than the name of the directory.
