Set highlighter to pygments when upgrading

In case you are upgrading from 1.4.2 to 2.0 and the pygments option is
set to true, then the highlighter option will be set to pygments
automatically.

lib/jekyll/configuration.rb

@@ -212,8 +212,11 @@ module Jekyll
       if config.has_key? 'pygments'
         Jekyll.logger.warn "Deprecation:", "The 'pygments' configuration option" +
                             " has been renamed to 'highlighter'. Please update your" +
-                            " config file accordingly. The allowed values are 'rouge"+
+                            " config file accordingly. The allowed values are 'rouge', " +
                             "'pygments' or null"
+
+        config['highlighter'] = 'pygments' if config['pygments']
+        config.delete('pygments')
       end
 
       %w[include exclude].each do |option|

test/test_configuration.rb

@@ -51,11 +51,12 @@ class TestConfiguration < Test::Unit::TestCase
   context "#backwards_compatibilize" do
     setup do
       @config = Configuration[{
-        "auto"    => true,
-        "watch"   => true,
-        "server"  => true,
-        "exclude" => "READ-ME.md, Gemfile,CONTRIBUTING.hello.markdown",
-        "include" => "STOP_THE_PRESSES.txt,.heloses, .git"
+        "auto"     => true,
+        "watch"    => true,
+        "server"   => true,
+        "exclude"  => "READ-ME.md, Gemfile,CONTRIBUTING.hello.markdown",
+        "include"  => "STOP_THE_PRESSES.txt,.heloses, .git",
+        "pygments" => true,
       }]
     end
     should "unset 'auto' and 'watch'" do
@@ -78,6 +79,11 @@ class TestConfiguration < Test::Unit::TestCase
       assert @config.backwards_compatibilize.has_key?("include")
       assert_equal @config.backwards_compatibilize["include"], %w[STOP_THE_PRESSES.txt .heloses .git]
     end
+    should "set highlighter to pygments" do
+      assert @config.has_key?("pygments")
+      assert !@config.backwards_compatibilize.has_key?("pygments")
+      assert_equal @config.backwards_compatibilize["highlighter"], "pygments"
+    end
   end
   context "#fix_common_issues" do
     setup do