chore(deps): update dependency c8 to v7 (#302)

Author: renovate-bot

packages/google-cloud-bigquery-datatransfer/package.json

@@ -46,7 +46,7 @@
   "devDependencies": {
     "@types/mocha": "^5.2.5",
     "@types/node": "^12.0.0",
-    "c8": "^6.0.0",
+    "c8": "^7.0.0",
     "eslint": "^6.0.0",
     "eslint-config-prettier": "^6.0.0",
     "eslint-plugin-node": "^11.0.0",