Bump 4.1.0 beta version in release notes

Author: michaelklishin

release-notes/4.1.0.md

@@ -1,6 +1,6 @@
-## RabbitMQ 4.1.0-beta.4
+## RabbitMQ 4.1.0-beta.5
 
-RabbitMQ 4.1.0-beta.4 is a preview release (in development) of a new feature release.
+RabbitMQ 4.1.0-beta.5 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.