Update .travis.yml

Added a gist to handle the submodule permissions (from http://stackoverflow.com/questions/15674064/github-submodule-access-rights-travis-ci)

Author: cp2boston

.travis.yml

@@ -3,6 +3,13 @@ install:
   - pip install tox 
 script:
   - tox
+# Handle git submodules yourself
+git:
+    submodules: false
+# Use sed to replace the SSH URL with the public URL, then initialize submodules
+before_install:
+    - sed -i 's/[email protected]:/https:\/\/github.com\//' .gitmodules
+    - git submodule update --init --recursive
 
 notifications:
   slack: