Bump concurrent-ruby from 1.3.5 to 1.3.6

Bumps [concurrent-ruby](https://github.com/ruby-concurrency/concurrent-ruby) from 1.3.5 to 1.3.6.
- [Release notes](https://github.com/ruby-concurrency/concurrent-ruby/releases)
- [Changelog](https://github.com/ruby-concurrency/concurrent-ruby/blob/master/CHANGELOG.md)
- [Commits](ruby-concurrency/concurrent-ruby@v1.3.5...v1.3.6)

---
updated-dependencies:
- dependency-name: concurrent-ruby
  dependency-version: 1.3.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -52,7 +52,7 @@ GEM
     codecov (0.6.0)
       simplecov (>= 0.15, < 0.22)
     coderay (1.1.3)
-    concurrent-ruby (1.3.5)
+    concurrent-ruby (1.3.6)
     connection_pool (2.5.4)
     diff-lcs (1.6.2)
     docile (1.4.1)