concurrent-ruby dropped logger dependency

Therefore we need to add the dependency to logger here.
See ruby-concurrency/concurrent-ruby#1062

Author: sbernhard

lib/smart_proxy_main.rb

@@ -1,6 +1,7 @@
 APP_ROOT = "#{__dir__}/.."
 
 require 'smart_proxy'
+require 'logger'
 require 'launcher'
 
 require 'fileutils'