Bump json from 1.7.6 to 1.8.6 in /matchbook

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>

matchbook/Gemfile.lock

@@ -54,7 +54,7 @@ GEM
     jquery-rails (2.2.0)
       railties (>= 3.0, < 5.0)
       thor (>= 0.14, < 2.0)
-    json (1.7.6)
+    json (1.8.6)
     mail (2.4.4)
       i18n (>= 0.4.0)
       mime-types (~> 1.16)