Update rack-test requirement from ~> 0.5 to ~> 1.1

Updates the requirements on [rack-test](https://github.com/rack-test/rack-test) to permit the latest version.
- [Release notes](https://github.com/rack-test/rack-test/releases)
- [Changelog](https://github.com/rack/rack-test/blob/master/History.md)
- [Commits](rack/rack-test@v0.5.0...v1.1.0)

---
updated-dependencies:
- dependency-name: rack-test
  dependency-type: direct:production
...

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

Gemfile

@@ -6,7 +6,7 @@ gem "json"
 
 gem "minitest", "~> 5.11"
 gem "mocha", "~> 1.11", require: false
-gem "rack-test", "~> 0.5"
+gem "rack-test", "~> 1.1"
 gem "rake"
 gem "rubocop", "~> 0.80"
 gem "pry"