ZOOKEEPER-3234: Add Travis-CI configuration file

Author: Enrico Olivelli <eolivelli@apache.org>

Reviewers: andor@apache.org

Closes #830 from eolivelli/fix/travis-3

.travis.yml

@@ -13,3 +13,5 @@ script: mvn clean install -DskipTests spotbugs:check
 branches:
   only:
   - master
+  - branch-3.5
+  - branch-3.4