Enable Travis for all branches

We are using branches for other flows of development, so we really want
it running everywhere.
diff --git a/.travis.yml b/.travis.yml
index e99f40d..e5348b1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -23,10 +23,6 @@
 os:
   - linux
 
-branches:
-  only:
-    - master
-
 notifications:
   email: false