chore(package): update babel-plugin-istanbul to version 5.1.4

Closes #92

Author: greenkeeper[bot]

package.json

@@ -52,7 +52,7 @@
     "babel-cli": "^6.18.0",
     "babel-core": "^6.18.0",
     "babel-eslint": "^8.0.0",
-    "babel-plugin-istanbul": "^4.1.1",
+    "babel-plugin-istanbul": "^5.1.4",
     "babel-plugin-transform-flow-strip-types": "^6.21.0",
     "babel-preset-env": "^1.1.8",
     "babel-register": "^6.18.0",