chore(package): add coverage reporter

package.json

@@ -8,7 +8,8 @@
     "test": "NODE_ENV=test mocha --compilers js:babel/register --require co-mocha 'src/**/*.spec.js'",
     "eslint": "eslint src",
     "prepublish": "npm test && npm run build",
-    "build": "rm -rf lib/* && babel src --ignore *.spec.js --out-dir lib"
+    "build": "rm -rf lib/* && babel src --ignore *.spec.js --out-dir lib",
+    "coverage": "NODE_ENV=test babel-istanbul --include-babel-polyfill cover _mocha 'src/**/*.spec.js'"
   },
   "author": "RisingStack",
   "repository": {
@@ -36,6 +37,7 @@
   "devDependencies": {
     "babel": "^5.8.23",
     "babel-eslint": "^4.1.3",
+    "babel-istanbul": "^0.3.20",
     "chai": "^3.3.0",
     "chai-subset": "^1.1.0",
     "co-mocha": "^1.1.2",
@@ -45,8 +47,7 @@
     "mongoose": "^4.1.11",
     "pre-commit": "^1.1.1",
     "sinon": "^1.17.1",
-    "sinon-chai": "^2.8.0",
-    "graphql": "^0.4.7"
+    "sinon-chai": "^2.8.0"
   },
   "pre-commit": [
     "test"