Bump babel-plugin-istanbul from 4.1.6 to 5.2.0

Bumps [babel-plugin-istanbul](https://github.com/istanbuljs/babel-plugin-istanbul) from 4.1.6 to 5.2.0.
- [Release notes](https://github.com/istanbuljs/babel-plugin-istanbul/releases)
- [Changelog](https://github.com/istanbuljs/babel-plugin-istanbul/blob/master/CHANGELOG.md)
- [Commits](https://github.com/istanbuljs/babel-plugin-istanbul/compare/v4.1.6...v5.2.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -73,7 +73,7 @@
     "babel-core": "^6.25.0",
     "babel-eslint": "^7.2.3",
     "babel-loader": "^7.1.1",
-    "babel-plugin-istanbul": "^4.1.1",
+    "babel-plugin-istanbul": "^5.2.0",
     "babel-plugin-transform-runtime": "^6.23.0",
     "babel-preset-env": "^1.6.0",
     "babel-preset-stage-0": "^6.24.1",