chore(deps): update dependency c8 to v7 (#493)

Author: renovate-bot

packages/google-cloud-dialogflow/package.json

@@ -44,7 +44,7 @@
     "protobufjs": "^6.8.0"
   },
   "devDependencies": {
-    "c8": "^6.0.1",
+    "c8": "^7.0.0",
     "codecov": "^3.0.0",
     "eslint": "^6.0.0",
     "eslint-config-prettier": "^6.0.0",