chore(deps): bump lockbox from 0.6.6 to 0.6.8

Bumps [lockbox](https://github.com/ankane/lockbox) from 0.6.6 to 0.6.8.
- [Release notes](https://github.com/ankane/lockbox/releases)
- [Changelog](https://github.com/ankane/lockbox/blob/master/CHANGELOG.md)
- [Commits](ankane/lockbox@v0.6.6...v0.6.8)

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

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -70,7 +70,7 @@ GEM
       concurrent-ruby (~> 1.0)
     ipaddr (1.2.3)
     jwt (2.3.0)
-    lockbox (0.6.6)
+    lockbox (0.6.8)
     mail (2.7.1)
       mini_mime (>= 0.1.1)
     mini_mime (1.1.2)