changed regex for matching user mentions

app/services/flavored_markdown.rb

@@ -6,7 +6,7 @@ class FlavoredMarkdown < Redcarpet::Render::HTML
   end
 
   def wrap_mentions(text)
-    text.gsub! /(^|\s)(@\w+)/ do
+    text.gsub! /(^|\s)(@[a-zA-Z0-9_]{1,16})/ do
       "#{$1}[#{$2}](#{show_user_profile_path $2.tr('@', '')})"
     end
     text