Bump json from 1.7.6 to 1.8.6

Bumps [json](https://github.com/flori/json) from 1.7.6 to 1.8.6.
- [Release notes](https://github.com/flori/json/releases)
- [Changelog](https://github.com/flori/json/blob/master/CHANGES.md)
- [Commits](flori/json@v1.7.6...v1.8.6)

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

Gemfile.lock

@@ -54,7 +54,7 @@ GEM
       activesupport (>= 4.2.0)
     i18n (0.9.5)
       concurrent-ruby (~> 1.0)
-    json (1.7.6)
+    json (1.8.6)
     loofah (2.18.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)