Bump concurrent-ruby from 1.1.5 to 1.3.7

Bumps [concurrent-ruby](https://github.com/ruby-concurrency/concurrent-ruby) from 1.1.5 to 1.3.7.
- [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@v1.1.5...v1.3.7)

---
updated-dependencies:
- dependency-name: concurrent-ruby
  dependency-version: 1.3.7
  dependency-type: indirect
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -8,7 +8,7 @@ GEM
     addressable (2.9.0)
       public_suffix (>= 2.0.2, < 8.0)
     colorator (1.1.0)
-    concurrent-ruby (1.1.5)
+    concurrent-ruby (1.3.7)
     em-websocket (0.5.1)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)