ci: Install all extras on travis

To successfully run the tests, we better install all extras on travis.
In particular MSIS was missing for the level-2 integration tests.

Author: st-bender

.travis.yml

@@ -27,7 +27,7 @@ install:
   - pip install -U pytest pytest-cov codecov coveralls
   - pip install tox-travis
   - pip install scrutinizer-ocular
-  - pip install -e .
+  - pip install -e ".[all]"
 script:
   - py.test -v --cov sciapy
 after_success: