Bump commander from 6.2.0 to 6.2.1 (#144)

Bumps [commander](https://github.com/tj/commander.js) from 6.2.0 to 6.2.1.
- [Release notes](https://github.com/tj/commander.js/releases)
- [Changelog](https://github.com/tj/commander.js/blob/master/CHANGELOG.md)
- [Commits](tj/commander.js@v6.2.0...v6.2.1)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -37,7 +37,7 @@
   },
   "homepage": "https://github.com/igorshubovych/markdownlint-cli#readme",
   "dependencies": {
-    "commander": "~6.2.0",
+    "commander": "~6.2.1",
     "deep-extend": "~0.6.0",
     "get-stdin": "~8.0.0",
     "glob": "~7.1.6",