Prefer DYNO name over system hostname on Heroku, fixes #1742

Changes.md

@@ -1,3 +1,9 @@
+3.1.3
+-----------
+
+- Use ENV['DYNO'] on Heroku for hostname display, rather than an ugly UUID. [#1742]
+
+
 3.1.2
 -----------
 

lib/sidekiq/util.rb

@@ -27,7 +27,7 @@ module Sidekiq
     end
 
     def hostname
-      Socket.gethostname
+      ENV['DYNO'] || Socket.gethostname
     end
 
     def identity