Bump http from 0.1.18 to 0.1.21

Bumps [http](https://github.com/hyperium/http) from 0.1.18 to 0.1.21.
- [Release notes](https://github.com/hyperium/http/releases)
- [Changelog](https://github.com/hyperium/http/blob/v0.1.21/CHANGELOG.md)
- [Commits](hyperium/http@v0.1.18...v0.1.21)

---
updated-dependencies:
- dependency-name: http
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]