Bump httparty from 0.20.0 to 0.21.0

Bumps [httparty](https://github.com/jnunemaker/httparty) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/jnunemaker/httparty/releases)
- [Changelog](https://github.com/jnunemaker/httparty/blob/master/Changelog.md)
- [Commits](https://github.com/jnunemaker/httparty/compare/v0.20.0...v0.21.0)

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

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

Gemfile.lock

@@ -301,8 +301,8 @@ GEM
     highline (2.0.3)
     html_tokenizer (0.0.7)
     htmlentities (4.3.4)
-    httparty (0.20.0)
-      mime-types (~> 3.0)
+    httparty (0.21.0)
+      mini_mime (>= 1.0.0)
       multi_xml (>= 0.5.2)
     httpi (2.5.0)
       rack