Configure travis-ci to ship alpha versions. (#106)

Author: elliotykim

.travis.yml

@@ -20,4 +20,4 @@ cache:
 branches:
   only:
   - master
-  - /^\d+\.\d+\.\d+(-SNAPSHOT)?$/ # trigger builds on tags which are semantically versioned to ship the SDK.
+  - /^\d+\.\d+\.\d+(-SNAPSHOT|-alpha)?$/ # trigger builds on tags which are semantically versioned to ship the SDK.