chore(package): update coveralls to version 2.13.0

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -47,7 +47,7 @@
   "homepage": "https://github.com/zeit/micro#readme",
   "devDependencies": {
     "ava": "0.18.2",
-    "coveralls": "2.12.0",
+    "coveralls": "2.13.0",
     "eslint-config-prettier": "1.5.0",
     "husky": "0.13.3",
     "lint-staged": "3.4.0",