chore(package): update istanbul to version 0.4.2

http://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -60,7 +60,7 @@
   "devDependencies": {
     "concat-stream": "^1.5.0",
     "coveralls": "^2.11.5",
-    "istanbul": "^0.4.0",
+    "istanbul": "^0.4.2",
     "jsdoc": "^3.4.0",
     "jshint": "^2.8.0",
     "mocha": "^2.3.4",