fix(npm): downgrade untildify@2

Support Node.js 0.12 again

Author: azu

package.json

@@ -35,7 +35,7 @@
     "prh": "^1.0.1",
     "structured-source": "^3.0.2",
     "textlint-rule-helper": "^1.1.3",
-    "untildify": "^3.0.2"
+    "untildify": "^2.0.0"
   },
   "devDependencies": {
     "babel-cli": "^6.7.5",