Upgrade javamelody-core to 1.81.0
Upgrade javamelody-core to 1.81.0

This upgrade includes both fixes and additions - [1].

[1] https://github.com/javamelody/javamelody/wiki/ReleaseNotes#1810

Change-Id: I95262385f7f0a5c77af9d349e5552f77faa05914

GerritCodeReview/plugins_javamelody,GerritCodeReview/plugins_javamelody,GerritCodeReview/plugins_javamelody