Add codecov as devDependency

Author: AndrewJo

package.json

@@ -20,6 +20,7 @@
   "devDependencies": {
     "broccoli-asset-rev": "^2.2.0",
     "chai": "^3.5.0",
+    "codecov": ">1.0.0",
     "ember-cli": "1.13.13",
     "ember-cli-app-version": "^1.0.0",
     "ember-cli-content-security-policy": "0.4.0",