groups: balance deduction cleanup

src/app/groups.coffee

@@ -25,15 +25,13 @@ module.exports.app = (appExports, model, app) ->
       return model.add 'groups', newGroup, ->location.reload()
 
     # guilds - 4G
-    balance = user.get('balance')
-    unless balance >= 1
+    unless user.get('balance') >= 1
       return $('#more-gems-modal').modal 'show'
     if confirm "Create Guild for 4 Gems?"
       newGroup.privacy = (model.get("_new.group.privacy") || 'public') if type is 'guild'
       newGroup.balance = 1 # they spent $ to open the guild, it goes into their guild bank
       model.add 'groups', newGroup, ->
-        user.set 'balance', (balance - 1)
-        location.reload()
+        user.incr 'balance', -1, ->location.reload()
 
   appExports.toggleGroupEdit = (e, el) ->
     path = "_editing.groups.#{$(el).attr('data-gid')}"