Update dependency eslint to v7

Author: renovate-bot

source/SIL.AppBuilder.Portal.Frontend/package.json

@@ -151,7 +151,7 @@
     "css-loader": "^4.0.0",
     "dotenv": "^8.0.0",
     "ember-cli": "^3.8.1",
-    "eslint": "^5.8.0",
+    "eslint": "^7.0.0",
     "eslint-config-prettier": "^3.1.0",
     "eslint-config-typescript": "^3.0.0",
     "eslint-plugin-import": "^2.14.0",