feat: update istanbul

See gotwarlost/istanbul#15

Author: mrzepinski

package.json

@@ -19,7 +19,7 @@
   ],
   "author": "SATO taichi <ryushi@gmail.com>",
   "dependencies": {
-    "istanbul": "~0.1.45",
+    "istanbul": "~0.2.3",
     "ibrik":  "~1.0.1",
     "dateformat": "~1.0.6"
   },