chore(deps): update dependency babel-plugin-istanbul to v5

Author: renovate-bot

package.json

@@ -28,7 +28,7 @@
     "ava": "0.25.0",
     "babel-cli": "6.26.0",
     "babel-core": "6.26.3",
-    "babel-plugin-istanbul": "4.1.6",
+    "babel-plugin-istanbul": "5.1.0",
     "babel-plugin-transform-es2015-modules-umd": "6.24.1",
     "babel-preset-es2015": "6.24.1",
     "babel-preset-stage-3": "6.24.1",