Update dependency superagent to v5.2.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
superagent	dependencies	minor	5.1.3 -> 5.2.1

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Release Notes

visionmedia/superagent

### [`v5.2.1`](https://togithub.com/visionmedia/superagent/releases/v5.2.1) [Compare Source](https://togithub.com/visionmedia/superagent/compare/v5.2.0...v5.2.1) - fix: fixed .buffer prototype in client issue (closes [#​1517](https://togithub.com/visionmedia/superagent/issues/1517)) [`639ce2c`](https://togithub.com/visionmedia/superagent/commit/639ce2c) ### [`v5.2.0`](https://togithub.com/visionmedia/superagent/releases/v5.2.0) [Compare Source](https://togithub.com/visionmedia/superagent/compare/v5.1.4...v5.2.0) - Check res.text as well to return a better error txt message ([#​1534](https://togithub.com/visionmedia/superagent/issues/1534)) [`d957c81`](https://togithub.com/visionmedia/superagent/commit/d957c81) ### [`v5.1.4`](https://togithub.com/visionmedia/superagent/releases/v5.1.4) [Compare Source](https://togithub.com/visionmedia/superagent/compare/v5.1.3...v5.1.4) - fix: throw timeout error in promise interface when timedout ([#​1510](https://togithub.com/visionmedia/superagent/issues/1510)) [`56ce517`](https://togithub.com/visionmedia/superagent/commit/56ce517)

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