Update httparty to >= 0.21.0

[cjmartian]

Overview

This pull request updates httparty to >= 0.21.0

Checklist

• [ ] Make sure that all of the tests pass, and fix any that don't. Just run rake in your checkout directory, or review the CI job triggered whenever you push to a pull request.
• [ ] Make sure that there is 100% test coverage by running rake coverage:spec or ignoring untestable sections of code with # :nocov comments. If you need help getting to 100% coverage please ask; however, don't just submit code with no tests.
• [ ] If you have added a new command line option, we would greatly appreciate a corresponding integration test that exercises it from start to finish. This is optional but recommended.
• [ ] If you have added any new gem dependencies, make sure those gems are licensed under the MIT or Apache 2.0 license. We cannot add any dependencies on gems licensed under GPL.
• [ ] If you have added any new gem dependencies, make sure you've checked in a copy of the .gem file into the vendor/cache directory.

/cc [related issues] [teams and individuals, making sure to mention why you're CC-ing them]

[cjmartian]

Removed ssl_ca mismatch test. HTTParty turns on verification by default if the url begins with https or if the port is 443.