Upgrade markdownlint-cli to latest

Author: mroderick

package.json

@@ -53,7 +53,7 @@
     "eslint-plugin-mocha": "^4.2.0",
     "husky": "^0.14.2",
     "lint-staged": "^6.0.0",
-    "markdownlint-cli": "^0.4.0",
+    "markdownlint-cli": "^0.6.0",
     "mocha": "^4.0.0",
     "mochify": "^5.1.0",
     "mochify-istanbul": "^2.4.1",