chore(deps): update dependency babel-plugin-istanbul to v7

Author: renovate[bot]

package.json

@@ -13,7 +13,7 @@
     "@commitlint/config-conventional": "8.3.4",
     "ava": "3.15.0",
     "babel-cli": "6.26.0",
-    "babel-plugin-istanbul": "4.1.6",
+    "babel-plugin-istanbul": "7.0.1",
     "babel-preset-env": "1.7.0",
     "babel-register": "6.26.0",
     "eslint": "5.16.0",