minor #11947 Change SimpleBus url (Arman-Hosseini)

This PR was submitted for the 4.1 branch but it was merged into the 4.2 branch instead (closes #11947).

Discussion
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Change SimpleBus url

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Commits
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f906061 Change SimpleBus url

Author: javiereguiluz

components/messenger.rst

@@ -312,4 +312,4 @@ Learn more
     /messenger/*
 
 .. _blog posts about command buses: https://matthiasnoback.nl/tags/command%20bus/
-.. _SimpleBus project: http://simplebus.io
+.. _SimpleBus project: http://docs.simplebus.io/en/latest/