chore(package): update codecov to version 2.3.1

Closes #10

Author: greenkeeper[bot]

package.json

@@ -12,7 +12,7 @@
   "devDependencies": {
     "ava": "^0.16.0",
     "babel-eslint": "^7.1.0",
-    "codecov": "^1.0.1",
+    "codecov": "^2.3.1",
     "cross-env": "^3.1.3",
     "doctoc": "^1.2.0",
     "nyc": "^8.4.0",