Bump chartkick from 5.0.4 to 5.0.6

Bumps [chartkick](https://github.com/ankane/chartkick) from 5.0.4 to 5.0.6.
- [Changelog](https://github.com/ankane/chartkick/blob/master/CHANGELOG.md)
- [Commits](ankane/chartkick@v5.0.4...v5.0.6)

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

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

Gemfile.lock

@@ -96,7 +96,7 @@ GEM
       rack-test (>= 0.6.3)
       regexp_parser (>= 1.5, < 3.0)
       xpath (~> 3.2)
-    chartkick (5.0.4)
+    chartkick (5.0.6)
     concurrent-ruby (1.2.2)
     connection_pool (2.4.1)
     crass (1.0.6)