Force binary sckit-learn for travis

.travis.yml

@@ -6,7 +6,7 @@ python:
   - "3.5"
   - "3.6"
 install:
-  - pip install --only-binary=numpy,scipy numpy scipy
+  - pip install --only-binary=numpy,scipy,scikit-learn numpy scipy scikit-learn
   - pip install flake8
   - python setup.py install
 script: pytest --cov