Add explicit dependency on @types/unist

Reviewed-by: Christian Murphy <[email protected]>
Reviewed-by: Remco Haszing <[email protected]>
Reviewed-by: Titus Wormer <[email protected]>

Closes GH-146.

Author: GuiltyDolphin

package.json

@@ -46,6 +46,7 @@
     "index.js"
   ],
   "dependencies": {
+    "@types/unist": "^2.0.0",
     "bail": "^2.0.0",
     "extend": "^3.0.0",
     "is-buffer": "^2.0.0",