Fix typo in error message (#535)

app/jobs/unqueue_message_job.rb

@@ -430,7 +430,7 @@ class UnqueueMessageJob < Postal::Job
               Raven.capture_exception(e, :extra => {:job_id => self.id, :server_id => queued_message.server_id, :message_id => queued_message.message_id})
             end
             if queued_message.message
-              queued_message.message.create_delivery("Error", :details => "An internal error occurred while sending this message. This message will be retried automatically. This this persists, contact support for assistance.", :output => "#{e.class}: #{e.message}", :log_id => "J-#{self.id}")
+              queued_message.message.create_delivery("Error", :details => "An internal error occurred while sending this message. This message will be retried automatically. If this persists, contact support for assistance.", :output => "#{e.class}: #{e.message}", :log_id => "J-#{self.id}")
             end
           end
         end