Update dependency c8 to v7 (#255)

Author: renovate-bot

package.json

@@ -49,7 +49,7 @@
     "@types/temp-write": "3.3.0",
     "ava": "2.4.0",
     "builtins": "3.0.0",
-    "c8": "6.0.1",
+    "c8": "7.0.0",
     "codecov": "3.6.1",
     "husky": "3.1.0",
     "lint-staged": "9.5.0",