chore(package): update babel-plugin-transform-class-properties to version 6.18.0 (#2312)

https://greenkeeper.io/ [skip ci]

Author: greenkeeperio-bot

Diff for: package.json

@@ -58,7 +58,7 @@
     "yeoman-welcome": "^1.0.1"
   },
   "devDependencies": {
-    "babel-plugin-transform-class-properties": "^6.16.0",
+    "babel-plugin-transform-class-properties": "^6.18.0",
     "babel-preset-es2015": "^6.18.0",
     "chai": "^3.2.0",
     "del": "^2.2.0",