travis: For later workflow consider selective building

Only certain branches and pull requests.

.travis.yml

@@ -25,6 +25,14 @@ env:
   - DB=pgsql DIRECTOR_TESTDB_RES="Director PostgreSQL TestDB" DIRECTOR_TESTDB="director_test"
     DIRECTOR_TESTDB_USER="director_test"
 
+# Consider when migrating to PRs
+#branches:
+#  only:
+#  - master
+#  - next
+#  - /^support\//
+#  - /^v\d/
+
 before_script:
   - ./test/setup_vendor.sh
   - ./test/travis-prepare.sh