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
diff --git a/external_plugin_deps.bzl b/external_plugin_deps.bzl
index 863d1ab..e41712a 100644
--- a/external_plugin_deps.bzl
+++ b/external_plugin_deps.bzl
@@ -3,8 +3,8 @@
 def external_plugin_deps():
     maven_jar(
         name = "javamelody-core",
-        artifact = "net.bull.javamelody:javamelody-core:1.80.0",
-        sha1 = "9499869f068a1e57efefa392a06b5a7635613359",
+        artifact = "net.bull.javamelody:javamelody-core:1.81.0",
+        sha1 = "0514c4ab7b8f482b29fe5bf1c140508a05012a4f",
     )
 
     maven_jar(