Update dependency superagent to v5.1.2

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
superagent	dependencies	patch	5.1.1 -> 5.1.2

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Release Notes

visionmedia/superagent

### [`v5.1.2`](https://togithub.com/visionmedia/superagent/releases/v5.1.2) [Compare Source](https://togithub.com/visionmedia/superagent/compare/v5.1.1...v5.1.2) - fix: fixed linting, fixed deprecation warning in tests [`7d70a75`](https://togithub.com/visionmedia/superagent/commit/7d70a75) - Use `res.getHeaders()` to avoid deprecation warning ([#​1503](https://togithub.com/visionmedia/superagent/issues/1503)) [`8dc8b91`](https://togithub.com/visionmedia/superagent/commit/8dc8b91)

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