Reactivate travis on all branches. (#607)

limiting only to master means that forks do not run tests except on
master.

This was presumably done originally as development of feature branches
and stable were on the same repo, as everyone is going through PRs this
seem unnecesasry now.

Author: Carreau

.travis.yml

@@ -1,9 +1,5 @@
 language: python
 
-branches:
-  only:
-    - master
-
 sudo: false
 
 addons: