Update eslint requirement from 5.12.0 to 5.15.0 (#4394)

Updates the requirements on [eslint](https://github.com/eslint/eslint) to permit the latest version.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](https://github.com/eslint/eslint/compare/v5.12.0...v5.15.0)

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

package.json

@@ -118,7 +118,7 @@
 		"elasticsearch": "15.3.1",
 		"emojilib": "2.4.0",
 		"escape-regexp": "0.0.1",
-		"eslint": "5.12.0",
+		"eslint": "5.15.0",
 		"eslint-plugin-vue": "5.2.2",
 		"eventemitter3": "3.1.0",
 		"feed": "2.0.2",