When pygments is required after Jekyll::Logger is required, its internal require to Ruby's stdlib Logger class chokes. This is an ugly-ass work-around.

lib/jekyll/logger.rb

@@ -1,5 +1,7 @@
+require 'logger'
+
 module Jekyll
-  module Logger
+  class Logger < Logger
     # Public: Print a jekyll message to stdout
     #
     # topic - the topic of the message, e.g. "Configuration file", "Deprecation", etc.