fix travis docs check (#4556)

.travis.yml

@@ -7,9 +7,6 @@ cache:
   - node_modules
 before_install:
 - |
-    if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then
-      TRAVIS_COMMIT_RANGE="FETCH_HEAD...$TRAVIS_BRANCH"
-    fi
     git diff --name-only $TRAVIS_COMMIT_RANGE | grep -qvE '(\.md$)|(^(doc))/' || {
       echo "Only docs were updated, stopping build process."
       exit