chore: Enable Travis builds on release branches. (#217)

Author: mikeproeng37

.travis.yml

@@ -23,6 +23,6 @@ cache:
 branches:
   only:
   - master
-  - /^\d+\.\d+\.\d+(-SNAPSHOT|-alpha|-beta)?\d*$/ # trigger builds on tags which are semantically versioned to ship the SDK.
+  - /^\d+\.\d+\.(\d|[x])+(-SNAPSHOT|-alpha|-beta)?\d*$/ # trigger builds on tags which are semantically versioned to ship the SDK.
 after_success:
   - ./gradlew coveralls uploadArchives --console plain