Bump http from 0.13.4 to 0.13.6

Bumps [http](https://github.com/dart-lang/http/tree/master/pkgs) from 0.13.4 to 0.13.6.
- [Release notes](https://github.com/dart-lang/http/releases)
- [Commits](https://github.com/dart-lang/http/commits/http-v0.13.6/pkgs)

---
updated-dependencies:
- dependency-name: http
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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