chore(deps-dev): bump markdownlint-cli from 0.20.0 to 0.21.0 (#529)

Author: dependabot-preview[bot]

package.json

@@ -89,7 +89,7 @@
     "execa": "4.0.0",
     "husky": "3.1.0",
     "lint-staged": "9.5.0",
-    "markdownlint-cli": "0.20.0",
+    "markdownlint-cli": "0.21.0",
     "npm-run-all": "4.1.5",
     "prettier": "1.19.1",
     "rollup": "1.28.0",