Merge pull request #2132 from mozilla/greenkeeper/babel-plugin-istanbul-4.1.1

Update babel-plugin-istanbul to the latest version 🚀

package.json

@@ -226,7 +226,7 @@
     "babel-eslint": "7.1.0",
     "babel-gettext-extractor": "git+https://github.com/muffinresearch/babel-gettext-extractor.git#0d39d3882bc846e7dcb6c9ff6463896c96920ce6",
     "babel-loader": "6.3.2",
-    "babel-plugin-istanbul": "4.0.0",
+    "babel-plugin-istanbul": "4.1.1",
     "babel-plugin-react-transform": "2.0.2",
     "babel-plugin-transform-class-properties": "6.18.0",
     "babel-plugin-transform-decorators-legacy": "1.3.4",