Fix the branch name that Travis uses

Author: Seulgi Kim

.travis/check-change

@@ -84,7 +84,7 @@ push)
         # we can find common ancestor of master and the branch.
         echo "Branch push"
         git fetch origin master:master;
-        COMMIT_RANGE="origin/master..${TRAVIS_COMMIT}"
+        COMMIT_RANGE="master..${TRAVIS_COMMIT}"
     fi
     ;;
 pull_request)