fix .travis.yml for celegans

.travis.yml

@@ -36,7 +36,7 @@ install:
   - pip install python-coveralls pytest-cov
   - pip install keras==2.0.4
   - pip install matplotlib seaborn
-  - pip install observations sklearn
+  - pip install networkx==1.9.1 observations sklearn
   - pip install tensorflow==1.3.0
   - pip install nbformat nbconvert jupyter_client jupyter
   - python setup.py install