Finish migration to pnpm

Author: dprothero

src/package.json

@@ -32,7 +32,9 @@
     "cheerio": "^1.0.0-rc.12",
     "hast-util-to-html": "^9.0.0",
     "hast-util-to-mdast": "^10.1.0",
+    "mdast-util-from-markdown": "^2.0.2",
     "mdast-util-gfm": "^3.0.0",
+    "mdast-util-to-markdown": "^2.1.2",
     "mdast-util-to-string": "^3.2.0",
     "micromark-extension-gfm": "^3.0.0",
     "pandoc-wrapper": "^0.3.1",