fix(coverage): Fix coverage report scripts

It's tricky to configure istanbul to get coverage from es2015 code. However the nyc wrapper seems to
work fine without much configuration effort.

.gitignore

@@ -3,6 +3,7 @@ node_modules
 
 # test coverage report files
 coverage
+.nyc_output
 
 # vim swap files
 *.swp

package.json

@@ -4,13 +4,15 @@
   "main": "dist/index.js",
   "scripts": {
     "build": "babel -d dist src",
-    "cover": "istanbul cover _mocha -- test.js",
-    "coveralls": "istanbul cover --report lcovonly _mocha -- test.js && cat ./coverage/lcov.info | coveralls && rm -rf ./coverage",
+    "cover": "nyc npm test",
+    "coveralls": "npm run cover && npm run report:text | coveralls",
     "lint": "standard",
     "premultitest": "npm run lint",
     "multitest": "multitest",
     "prepublish": "npm run build",
     "pretest": "npm run lint",
+    "report:html": "nyc report --reporter=html",
+    "report:text": "nyc report --reporter=text-lcov",
     "test": "mocha --compilers js:babel-register test.js",
     "semantic-release": "semantic-release pre && npm publish && semantic-release post && git fetch --tags && pr-tagger --log-level debug --access-token ${GH_TOKEN}"
   },
@@ -37,9 +39,9 @@
     "coveralls": "2.11.6",
     "cz-conventional-changelog": "^1.1.5",
     "ghooks": "1.0.3",
-    "istanbul": "0.4.2",
     "mocha": "2.4.5",
     "multitest": "0.3.2",
+    "nyc": "5.5.0",
     "pr-tagger": "0.7.1",
     "semantic-release": "^4.3.5",
     "sinon": "1.17.3",