fix: support for hyphens in group name

The group mention @ORG-team triggers notifications for the group @ORG. This fix changes the RegExp, so that the group name is correctly extracted.

see: https://meta.discourse.org/t/group-mentions-that-begin-with-the-same-characters-may-be-incorrect/39892/12?u=rriemann

lib/pretty_text.rb

@@ -73,7 +73,7 @@ module PrettyText
   @ctx_init = Mutex.new
 
   def self.mention_matcher
-    Regexp.new("\\W@(\\w{#{SiteSetting.min_username_length},#{SiteSetting.max_username_length}})\\b")
+    Regexp.new("\\W@([\\w\\-]{#{SiteSetting.min_username_length},#{SiteSetting.max_username_length}})\\b")
   end
 
   def self.app_root