fix README delete error

Author: josler

README.md

@@ -64,7 +64,8 @@ user = intercom.users.find(:id => "1")
 # Create a user
 user = intercom.users.create(:email => "[email protected]", :name => "Bob Smith", :signed_up_at => Time.now.to_i)
 # Delete a user
-deleted_user = intercom.users.find(:id => "1").delete
+user = intercom.users.find(:id => "1")
+deleted_user = intercom.users.delete(user)
 # Update custom_attributes for a user
 user.custom_attributes["average_monthly_spend"] = 1234.56
 intercom.users.save(user)