Update issues_form_hook_listener.rb

Updating to the following conventions
https://github.com/bbatsov/ruby-style-guide

lib/issues_form_hook_listener.rb

@@ -19,7 +19,7 @@ class IssuesFormHookListener < Redmine::Hook::ViewListener
     QboItem.update_all
  
     # Check to see if there is a quickbooks user attached to the issue
-    if not context[:issue].qbo_customer_id.nil? then
+    if not context[:issue].qbo_customer_id.nil?
       selected_customer = context[:issue].qbo_customer_id
       selected_item = context[:issue].qbo_item_id
     end
@@ -32,4 +32,4 @@ class IssuesFormHookListener < Redmine::Hook::ViewListener
     return "<p>#{select_customer}</p> <p>#{select_item}</p>"
   end
 
-end
+end