Update .travis.yml

specify branches

Author: Luc

.travis.yml

@@ -4,7 +4,11 @@ language: bash
 
 os:
   - linux
-
+branches:
+  only:
+    - master
+    - stable-esp-module
+    
 before_install:
   - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -ac -screen 0 1280x1024x16"