Only require uglifier when precompiling

lib/gollum/assets.rb

@@ -1,10 +1,10 @@
 require 'octicons'
-require 'uglifier'
 
 module Precious
   module Assets
     MANIFEST = %w(app.js editor.js mermaid.js app.css criticmarkup.css fileview.css ie7.css print.css *.png *.jpg *.svg *.eot *.ttf)
     ASSET_URL = 'gollum/assets'
+    JS_COMPRESSOR = :uglify unless defined?(JS_COMPRESSOR)
 
     def self.sprockets(dir = File.dirname(File.expand_path(__FILE__)))
       env = Sprockets::Environment.new
@@ -17,7 +17,7 @@ module Precious
       env.append_path ::File.join(dir, 'public/gollum/images')
       env.append_path ::File.join(dir, 'public/gollum/fonts')
 
-      env.js_compressor  = ::Uglifier.new(harmony: true) unless Precious::App.development?
+      env.js_compressor  = Precious::Assets::JS_COMPRESSOR unless Precious::App.development?
       env.css_compressor = :scss
 
       env.context_class.class_eval do