RELEASING.md in slack-ruby-bot-0.10.2 vs RELEASING.md in slack-ruby-bot-0.10.3

@@ -5,9 +5,10 @@
 ### Release
 
 Run tests, check that all tests succeed locally.
 
 ```
+export CONCURRENCY=celluloid-io
 bundle install
 rake
 ```
 
 Check that the last build succeeded in [Travis CI](https://travis-ci.org/slack-ruby/slack-ruby-bot) for all supported platforms.