travis: also test release branch

(cherry picked from commit 7581513)

Author: mtf90

.travis.yml

@@ -18,6 +18,7 @@ branches:
   only:
   - master
   - develop
+  - release
 install: true # skip mvn install, because we essentially run the same command in the script routine
 script:
   - mvn install -B -Pcode-analysis,code-coverage,bundles