Bump chartkick from 5.0.5 to 5.0.6

Bumps [chartkick](https://github.com/ankane/chartkick) from 5.0.5 to 5.0.6.
- [Changelog](https://github.com/ankane/chartkick/blob/master/CHANGELOG.md)
- [Commits](ankane/chartkick@v5.0.5...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

@@ -108,7 +108,7 @@ GEM
       xpath (~> 3.2)
     case_transform (0.2)
       activesupport
-    chartkick (5.0.5)
+    chartkick (5.0.6)
     cliver (0.3.2)
     coderay (1.1.3)
     concurrent-ruby (1.2.3)