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](jnunemaker/httparty@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: httparty
  dependency-type: direct:production
...

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

Gemfile.lock

@@ -144,8 +144,8 @@ GEM
       activesupport (>= 4.2.0)
     hashie (3.6.0)
     http-2 (0.10.1)
-    httparty (0.20.0)
-      mime-types (~> 3.0)
+    httparty (0.21.0)
+      mini_mime (>= 1.0.0)
       multi_xml (>= 0.5.2)
     i18n (1.6.0)
       concurrent-ruby (~> 1.0)