UPGRADING.md in slack-ruby-bot-0.12.0 vs UPGRADING.md in slack-ruby-bot-0.13.0

- old
+ new

@@ -1,7 +1,15 @@
 Upgrading SlackRubyBot
 ======================
 
+### Upgrading to >= 0.13.0
+
+#### Minimum Ruby Version
+
+Ruby 2.3 or later is now required.
+
+See [#246](https://github.com/slack-ruby/slack-ruby-bot/pull/246) for more information.
+
 ### Upgrading to >= 0.12.0
 
 #### Remove any references to `SlackRubyBot::Server#restart!`
 
 We have removed `SlackRubyBot::Server#restart!` since the [`slack-ruby-client`](https://github.com/slack-ruby/slack-ruby-client/blob/master/CHANGELOG.md) now restarts any connection that was not intentionally stopped via `SlackRubyBot::Server#stop!`.