chore(package): update babel-plugin-transform-class-properties to version 6.9.0

https://greenkeeper.io/

Author: greenkeeperio-bot

Diff for: package.json

@@ -53,7 +53,7 @@
     "yeoman-welcome": "^1.0.1"
   },
   "devDependencies": {
-    "babel-plugin-transform-class-properties": "^6.6.0",
+    "babel-plugin-transform-class-properties": "^6.9.0",
     "babel-preset-es2015": "^6.6.0",
     "babel-register": "^6.6.5",
     "chai": "^3.2.0",