FIX: when logging metrics ensure we report a string key

FIX: when logging metrics ensure we report a string key

We are zeroing out the counter with String so we can not use Symbol here.

diff --git a/lib/mobystash/container.rb b/lib/mobystash/container.rb
index cfe1cbc..3da7359 100644
--- a/lib/mobystash/container.rb
+++ b/lib/mobystash/container.rb
@@ -264,7 +264,7 @@ module Mobystash
         event = event.deep_merge(metadata)
 
         @config.logstash_writer.send_event(event)
-        @config.log_entries_sent_counter.increment(container_name: @name, container_id: @id, stream: stream)
+        @config.log_entries_sent_counter.increment(container_name: @name, container_id: @id, stream: stream.to_s)
       end
     end
 

GitHub sha: 2ebd93f5