message: fix link to howto
diff: @@ -27,7 +27,7 @@ In addition, developers who use third party middleware plugins should carefully
  This version of Botkit deprecates the `receive_via_postback` and `interactive_replies` options
  that caused button clicks to be treated as typed messages. These and other small changes to the way Botkit emits events may require minor updates to some Botkit apps.
  -[Upgrading from Botkit 0.5 or lower? Read this guide!](howto/upgrade_05to06.md)
  +[Upgrading from Botkit 0.5 or lower? Read this guide!](docs/howto/upgrade_05to06.md)
  ## 0.5.8
  