Update dev-dependencies

Author: wooorm

package.json

@@ -37,7 +37,7 @@
   "devDependencies": {
     "acorn": "^8.0.0",
     "mdast-util-from-markdown": "^0.8.0",
-    "mdast-util-to-markdown": "^0.5.0",
+    "mdast-util-to-markdown": "^0.6.0",
     "micromark-extension-mdxjs-esm": "^0.1.0",
     "nyc": "^15.0.0",
     "prettier": "^2.0.0",