chore(deps): update dependency babel-plugin-istanbul to v6 (#1638)

Author: renovate[bot]

package.json

@@ -75,7 +75,7 @@
         "babel-loader": "^7.1.2",
         "babel-plugin-import": "^1.1.1",
         "babel-plugin-inline-import-data-uri": "^1.0.1",
-        "babel-plugin-istanbul": "^5.0.0",
+        "babel-plugin-istanbul": "^6.0.0",
         "babel-plugin-syntax-dynamic-import": "^6.18.0",
         "babel-plugin-syntax-jsx": "^6.18.0",
         "babel-plugin-transform-class-properties": "^6.24.1",