chore(deps-dev): bump babel-plugin-istanbul from 5.2.0 to 6.0.0

Bumps [babel-plugin-istanbul](https://github.com/istanbuljs/babel-plugin-istanbul) from 5.2.0 to 6.0.0.
- [Release notes](https://github.com/istanbuljs/babel-plugin-istanbul/releases)
- [Changelog](https://github.com/istanbuljs/babel-plugin-istanbul/blob/master/CHANGELOG.md)
- [Commits](istanbuljs/babel-plugin-istanbul@v5.2.0...v6.0.0)

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

package.json

@@ -48,7 +48,7 @@
     "@babel/core": "^7.0.0",
     "@babel/preset-env": "^7.0.0",
     "@babel/register": "^7.0.0",
-    "babel-plugin-istanbul": "^5.2.0",
+    "babel-plugin-istanbul": "^6.0.0",
     "babel-upgrade": "^1.0.1",
     "chai": "^4.2.0",
     "chai-as-promised": "^7.1.1",