Bump @typescript-eslint/eslint-plugin from 2.20.0 to 2.21.0

Bumps [@typescript-eslint/eslint-plugin](https://github.com/typescript-eslint/typescript-eslint/tree/HEAD/packages/eslint-plugin) from 2.20.0 to 2.21.0.
- [Release notes](https://github.com/typescript-eslint/typescript-eslint/releases)
- [Changelog](https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/CHANGELOG.md)
- [Commits](https://github.com/typescript-eslint/typescript-eslint/commits/v2.21.0/packages/eslint-plugin)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -59,7 +59,7 @@
     "@types/proj4": "2.5.0",
     "@types/sinon": "7.5.1",
     "@types/typeahead": "0.11.32",
-    "@typescript-eslint/eslint-plugin": "2.20.0",
+    "@typescript-eslint/eslint-plugin": "2.21.0",
     "@typescript-eslint/parser": "2.20.0",
     "angular": "1.7.9",
     "angular-animate": "1.7.9",