[bundler] Bump concurrent-ruby from 1.3.3 to 1.3.4

Bumps [concurrent-ruby](https://github.com/ruby-concurrency/concurrent-ruby) from 1.3.3 to 1.3.4.
- [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@v1.3.3...v1.3.4)

---
updated-dependencies:
- dependency-name: concurrent-ruby
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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

Gemfile.lock

@@ -4,7 +4,7 @@ GEM
     addressable (2.8.7)
       public_suffix (>= 2.0.2, < 7.0)
     colorator (1.1.0)
-    concurrent-ruby (1.3.3)
+    concurrent-ruby (1.3.4)
     em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0)