fix py2.7

.travis.yml

@@ -17,6 +17,7 @@ before_install:
   - export CC="gcc-4.9"
   - export CXX="g++-4.9"
 install:
+  - if [[ $TRAVIS_PYTHON_VERSION == 2.7 ]]; pip install future; fi
   - pip install numpy
   - pip install torch_nightly -f https://download.pytorch.org/whl/nightly/cpu/torch_nightly.html
   - pip install pycodestyle

setup.py

@@ -24,7 +24,7 @@ __version__ = '1.3.0'
 url = 'https://github.com/rusty1s/pytorch_scatter'
 
 install_requires = []
-setup_requires = ['pytest-runner', 'future']
+setup_requires = ['pytest-runner']
 tests_require = ['pytest', 'pytest-cov']
 
 setup(