prevent Travis caching (#590)

* change CI install

* change CI install

* change CI install

.travis.yml

@@ -70,8 +70,14 @@ before_script:
 script:
   # integration
   - tox --sitepackages
-  - pip install --editable .
+
   #- python setup.py install --dry-run --user
+  - virtualenv vEnv ;
+    source vEnv/bin/activate
+  - pip install --editable . ;
+    cd .. & python -c "import pytorch_lightning ; print(pytorch_lightning.__version__)"
+  - deactivate ;
+    rm -rf vEnv
 
 after_success:
   - coverage report