Update dependency eslint to v7

Author: renovate-bot

package.json

@@ -34,7 +34,7 @@
   "devDependencies": {
     "ava": "^3.1.0",
     "coveralls": "^3.0.0",
-    "eslint": "^6.8.0",
+    "eslint": "^7.0.0",
     "eslint-config-problems": "4.0.0",
     "nyc": "^15.0.0",
     "postcss-import": "^12.0.0",