changed travis to install test requirements

.travis.yml

@@ -21,7 +21,7 @@ matrix:
       after_success: skip
 install:
   - pip install --upgrade pip
-  - pip install .
+  - pip install -e .['test']
 script:
   - pytest --cov-report html --cov-report term --disable-pytest-warnings --cov=pytorch_widedeep tests/
   # - pytest tests