Add missing dependency for types

Closes GH-1.

Reviewed-by: Titus Wormer <tituswormer@gmail.com>

Author: Methuselah96

package.json

@@ -39,20 +39,20 @@
     "index.js"
   ],
   "dependencies": {
+    "mdast-util-from-markdown": "^1.0.0",
     "mdast-util-gfm-autolink-literal": "^1.0.0",
     "mdast-util-gfm-footnote": "^1.0.0",
     "mdast-util-gfm-strikethrough": "^1.0.0",
     "mdast-util-gfm-table": "^1.0.0",
-    "mdast-util-gfm-task-list-item": "^1.0.0"
+    "mdast-util-gfm-task-list-item": "^1.0.0",
+    "mdast-util-to-markdown": "^1.0.0"
   },
   "devDependencies": {
     "@types/tape": "^4.0.0",
     "c8": "^7.0.0",
     "github-slugger": "^1.0.0",
     "hast-util-to-html": "^8.0.0",
-    "mdast-util-from-markdown": "^1.0.0",
     "mdast-util-to-hast": "^12.0.0",
-    "mdast-util-to-markdown": "^1.0.0",
     "micromark-extension-gfm": "^2.0.0",
     "node-fetch": "^3.0.0",
     "prettier": "^2.0.0",