chore(package): add rimraf as a devDependency

Author: niieani

package.json

@@ -29,6 +29,7 @@
   "homepage": "https://github.com/easy-webpack/core#readme",
   "devDependencies": {
     "ava": "^0.16.0",
+    "rimraf": "^2.5.4",
     "semantic-release": "^4.3.5",
     "ts-node": "^1.1.0",
     "tslint": "^3.11.0",