Trouble installing dvc with pip: No matching distribution found for futures>=3.2.0 (from dvc)
I'm on a fresh ubuntu 18.04 and I want to install DVC. But I run into some dependency problems. Never had that problem before.
```
➤ virtualenv -p python3 .venv
➤ source .venv/bin/activate.fish
➤ pip install dvc
Collecting dvc
  Using cached https://files.pythonhosted.org/packages/d2/2d/117b6e99f4e7f0760d99944919d9dcaaeabfb6c6182a9c890b7260eec697/dvc-0.15.2-py2.py3-none-any.whl
Collecting pyasn1>=0.4.1 (from dvc)
  Using cached https://files.pythonhosted.org/packages/d1/a1/7790cc85db38daa874f6a2e6308131b9953feb1367f2ae2d1123bb93a9f5/pyasn1-0.4.4-py2.py3-none-any.whl
Collecting ply>=3.9 (from dvc)
  Using cached https://files.pythonhosted.org/packages/a3/58/35da89ee790598a0700ea49b2a66594140f44dec458c07e8e3d4979137fc/ply-3.11-py2.py3-none-any.whl
Collecting futures>=3.2.0 (from dvc)
  Could not find a version that satisfies the requirement futures>=3.2.0 (from dvc) (from versions: 0.2.python3, 0.1, 0.2, 1.0, 2.0, 2.1, 2.1.1, 2.1.2, 2.1.3, 2.1.4, 2.1.5, 2.1.6, 2.2.0, 3.0.0, 3.0.1, 3.0.2, 3.0.3, 3.0.4, 3.0.5, 3.1.0, 3.1.1)
No matching distribution found for futures>=3.2.0 (from dvc)
```
Here are all relevant version
```
➤ pip --version
pip 18.0 from /home/PATH/.venv/lib/python3.6/site-packages/pip (python 3.6)
➤ python --version
Python 3.6.5
➤ virtualenv --version
16.0.0
```
diff --git a/setup.py b/setup.py
index 97eb7e198..7a15f6ed0 100644
--- a/setup.py
+++ b/setup.py
@@ -23,11 +23,9 @@ install_requires = [
     "jsonpath-rw==1.4.0",
     "reflink==0.2.0",
     "requests>=2.18.4",
+    'futures; python_version == "2.7"',
 ]
 
-if sys.version_info[0] == 2:
-    install_requires.append("futures>=3.2.0")
-
 # Extra dependencies for remote integrations
 gs = [
     "google-cloud==0.32.0",
['setup.py']