Changed value of n to a string

Author: David Massad

lib/aws/session_store/dynamo_db/locking/base.rb

@@ -127,7 +127,7 @@ def created_attr
     # Update client with current time + max_stale.
     def expire_at
       max_stale = @config.max_stale || 0
-      { value: { n: (Time.now + max_stale).to_i }, action: 'PUT' }
+      { value: { n: "#{(Time.now + max_stale).to_i }", action: 'PUT' }
     end
 
     # Attribute for TTL expiration of session.