[Tests] use `nyc` over `istanbul-cli`

also add cross-env + babel-plugin-istanbul for better coverage reports

.babelrc

 {
-  "presets": ["airbnb"]
+  "presets": ["airbnb"],
+  "env": {
+    "test": {
+      "plugins": ["istanbul"]
+    }
+  }
 }

.istanbul.yml

-instrumentation:
-  root: "."
-  extensions: [".js", ".jsx"]
-  excludes: [
-    "node_modules/**",
-    "lib/**",
-    "public/**",
-    "test/**",
-    "coverage/**"
-  ]
-check:
-  global:
-    statements: 89
-    branches: 66
-    lines: 91
-    functions: 79

.nycrc

+{
+  "extension": [
+    ".js",
+    ".jsx"
+  ],
+  "include": [
+    "src"
+  ],
+  "require": [
+    "babel-register"
+  ],
+  "reporter": [
+    "text",
+    "lcov"
+  ],
+  "all": true,
+  "check-coverage": true,
+  "statements": 79,
+  "branches": 78,
+  "lines": 79,
+  "functions": 66,
+  "sourceMap": false,
+  "instrument": false
+}

package.json

@@ -9,12 +9,10 @@
     "build:css": "node-sass css/styles.scss lib/css/_datepicker.css",
     "build:svg": "webpack",
     "clean": "rimraf lib",
-    "cover": "npm run cover:clean && npm run cover:mocha && npm run cover:check",
-    "cover:clean": "rimraf coverage",
-    "cover:check": "babel-node ./node_modules/istanbul/lib/cli check-coverage",
-    "cover:mocha": "babel-node ./node_modules/istanbul/lib/cli cover node_modules/mocha/bin/_mocha -- --compilers js:babel-register,jsx:babel-register --require airbnb-js-shims --recursive ./test/_helpers test/**/*",
+    "precover": "rimraf coverage",
+    "cover": "cross-env NODE_ENV=test nyc npm run mocha test",
     "lint": "eslint --ext .js,.jsx src test",
-    "mocha": "mocha --compilers js:babel-register,jsx:babel-register --require airbnb-js-shims --recursive ./test/_helpers",
+    "mocha": "mocha ./test/_helpers",
     "react:clean": "rimraf node_modules/react node_modules/react-dom node_modules/react-addons-test-utils",
     "react:14": "rimraf node_modules/.bin/npm && npm run react:clean && npm i react@0.14 react-dom@0.14 react-addons-test-utils@0.14",
     "react:15": "rimraf node_modules/.bin/npm && npm run react:clean && npm i react@15 react-dom@15 react-addons-test-utils@15",
@@ -57,11 +55,13 @@
     "babel-cli": "^6.22.2",
     "babel-core": "^6.22.1",
     "babel-loader": "^6.4.1",
+    "babel-plugin-istanbul": "^4.1.1",
     "babel-plugin-syntax-jsx": "^6.18.0",
     "babel-preset-airbnb": "^2.2.0",
     "babel-register": "^6.22.0",
     "chai": "^3.5.0",
     "coveralls": "^2.12.0",
+    "cross-env": "^4.0.0",
     "enzyme": "^2.7.1",
     "eslint": "^3.17.1",
     "eslint-config-airbnb": "^14.1.0",
@@ -71,7 +71,6 @@
     "git-directory-deploy": "^1.5.1",
     "imports-loader": "^0.7.1",
     "in-publish": "^2.0.0",
-    "istanbul": "^1.1.0-alpha.1",
     "json-loader": "^0.5.4",
     "karma": "^1.4.0",
     "karma-chai": "^0.1.0",
@@ -84,6 +83,7 @@
     "mocha-wrap": "^2.1.0",
     "moment": "^2.17.1 && < 2.18.0",
     "node-sass": "^4.4.0",
+    "nyc": "^10.1.2",
     "raw-loader": "^0.5.1",
     "react": "^15.4.2",
     "react-addons-shallow-compare": "^15.4.2",

test/mocha.opts

+--compilers js:babel-register,jsx:babel-register
+--require airbnb-js-shims
+--recursive