Make travis silent

Travis will always build all branches. As we just have a .travis.yml
on master, travis will go ahead and checkout PHP-5.3. It fails and
then sends mails. We really don't want to get spammed, so we add
a .travis.yml that is just silent.

.travis.yml

@@ -0,0 +1,10 @@
+language: php
+
+php:
+    # We only specify one version so we only get one worker
+    - 5.4
+
+notifications:
+    email: false
+
+script: exit 0