Update dependency babel-plugin-istanbul to v5.1.0

Author: renovate-bot

package.json

@@ -81,7 +81,7 @@
     "babel-core": "6.26.3",
     "babel-eslint": "9.0.0",
     "babel-istanbul": "0.12.2",
-    "babel-plugin-istanbul": "5.0.1",
+    "babel-plugin-istanbul": "5.1.0",
     "babel-register": "6.26.0",
     "browser-sync": "2.24.7",
     "coveralls": "3.0.2",