Bump chartkick from 5.1.2 to 5.2.1

Bumps [chartkick](https://github.com/ankane/chartkick) from 5.1.2 to 5.2.1.
- [Changelog](https://github.com/ankane/chartkick/blob/master/CHANGELOG.md)
- [Commits](ankane/chartkick@v5.1.2...v5.2.1)

---
updated-dependencies:
- dependency-name: chartkick
  dependency-version: 5.2.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -94,7 +94,7 @@ GEM
       rack-test (>= 0.6.3)
       regexp_parser (>= 1.5, < 3.0)
       xpath (~> 3.2)
-    chartkick (5.1.2)
+    chartkick (5.2.1)
     concurrent-ruby (1.3.4)
     connection_pool (2.5.3)
     crass (1.0.6)