Update .travis.yml to build only master branch (#2340)
Update .travis.yml to build only master branch (#2340)

* Added master to the safelist branch in .travis.yml.
couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios