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] <[email protected]>

Author: dependabot-preview[bot]

package-lock.json

@@ -37,7 +37,7 @@
         "@babel/preset-env": "7.9.6",
         "@babel/register": "7.10.1",
         "ava": "2.4.0",
-        "babel-plugin-istanbul": "5.2.0",
+        "babel-plugin-istanbul": "6.0.0",
         "eslint": "6.8.0",
         "nyc": "14.1.1",
         "rollup": "1.32.0"