Run vale linter only if vale is installed

package.json

@@ -41,6 +41,7 @@
     "@changesets/cli": "^2.11.0",
     "@spotify/eslint-config-oss": "^1.0.1",
     "@spotify/prettier-config": "^8.0.0",
+    "command-exists": "^1.2.9",
     "concurrently": "^5.2.0",
     "fs-extra": "^9.0.0",
     "husky": "^4.2.3",
@@ -65,7 +66,7 @@
       "prettier --write"
     ],
     "*.md": [
-      "vale"
+      "node ./scripts/check-docs-quality"
     ]
   },
   "jest": {