Skip Travis when only markdown files are changed

Author: Seulgi Kim

.travis.yml

@@ -14,7 +14,7 @@ jobs:
       os: osx
       before_install:
         - SKIP=`.travis/check-mergify-merge` && if [[ "$SKIP" = "skip" ]]; then exit 0; fi
-        - SKIP=`.travis/check-change '^(docs|spec)/'` && if [[ "$SKIP" = "skip" ]]; then exit 0; fi
+        - SKIP=`.travis/check-change '(^(docs|spec)/|*.md)'` && if [[ "$SKIP" = "skip" ]]; then exit 0; fi
         - SKIP=`.travis/check-change '^test/'` && if [[ "$SKIP" = "noskip" ]]; then RUN_UNIT_TEST=1; fi
       install:
         - nvm install 10