chore(deps): update dependency babel-plugin-istanbul to v6

| datasource | package               | from  | to    |
| ---------- | --------------------- | ----- | ----- |
| npm        | babel-plugin-istanbul | 5.2.0 | 6.0.0 |

Author: renovate-bot

package.json

@@ -25,7 +25,7 @@
     "@types/react": "16.9.19",
     "@types/react-dom": "16.9.5",
     "babel-loader": "8.0.6",
-    "babel-plugin-istanbul": "5.2.0",
+    "babel-plugin-istanbul": "6.0.0",
     "babel-plugin-styled-components": "1.10.7",
     "concurrently": "5.0.2",
     "cypress": "3.8.3",