Update puma requirement from ~> 6.1 to >= 6.1, < 8.0 (#419)

Updates the requirements on [puma](https://github.com/puma/puma) to permit the latest version.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v6.1.0...v7.0.1)

---
updated-dependencies:
- dependency-name: puma
  dependency-version: 7.0.1
  dependency-type: direct:production
...

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Author: dependabot[bot]

gemstash.gemspec

@@ -37,7 +37,7 @@ you push your own private gems as well."
   spec.add_runtime_dependency "faraday_middleware", "~> 1.0"
   spec.add_runtime_dependency "lru_redux", "~> 1.1"
   spec.add_runtime_dependency "psych", ">= 3.2.1"
-  spec.add_runtime_dependency "puma", "~> 6.1"
+  spec.add_runtime_dependency "puma", ">= 6.1", "< 8.0"
   spec.add_runtime_dependency "sequel", "~> 5.0"
   spec.add_runtime_dependency "server_health_check-rack", "~> 0.1"
   spec.add_runtime_dependency "sinatra", ">= 1.4", "< 5.0"