Bump superagent from 5.0.6 to 5.2.1

Bumps [superagent](https://github.com/visionmedia/superagent) from 5.0.6 to 5.2.1.
- [Release notes](https://github.com/visionmedia/superagent/releases)
- [Changelog](https://github.com/visionmedia/superagent/blob/master/HISTORY.md)
- [Commits](https://github.com/visionmedia/superagent/compare/v5.0.6...v5.2.1)

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

package.json

@@ -53,7 +53,7 @@
     "sass-loader": "^7.0.1",
     "sequelize": "^5.15.1",
     "spotify-web-api-node": "^4.0.0",
-    "superagent": "^5.0.6",
+    "superagent": "^5.2.1",
     "vue": "^2.6.11",
     "vue-loader": "^15.8.3",
     "vue-router": "^3.0.1",