4.1.0 release notes: we're at rc.1

(cherry picked from commit 13542dc)

Author: michaelklishin

release-notes/4.1.0.md

@@ -1,6 +1,6 @@
-## RabbitMQ 4.1.0-beta.5
+## RabbitMQ 4.1.0-rc.1
 
-RabbitMQ 4.1.0-beta.5 is a preview release (in development) of a new feature release.
+RabbitMQ 4.1.0-rc.1 is a preview release (in development) of a new feature release.
 
 See Compatibility Notes below to learn about **breaking or potentially breaking changes** in this release.