chore(deps): update dependency c8 to v7 (#38)

Author: renovate-bot

cloudbuild/package.json

@@ -18,7 +18,7 @@
     "@google-cloud/cloudbuild": "^1.3.0"
   },
   "devDependencies": {
-    "c8": "^6.0.1",
+    "c8": "^7.0.0",
     "chai": "^4.2.0",
     "mocha": "^6.0.0"
   }