Fix case statement

It failed with
 	undefined method `start_with?'

src/api/app/models/event/service_fail.rb

@@ -28,7 +28,7 @@ def metric_measurement
 
     def metric_tags
       error = case payload['error']
-              when start_with?('bad link:')
+              when /^bad link:/
                 'bad_link'
               when /^ 400 remote error:.*.service  No such file or directory/
                 'service_missing'