Fix keywords loading issue in Matlab

The issue is picked up via Dingus website.

NameError - uninitialized constant Rouge::Lexers::Matlab

Author: tancnle

lib/rouge/lexers/matlab.rb

@@ -19,11 +19,7 @@ def self.keywords
         )
       end
 
-      # self-modifying method that loads the builtins file
-      def self.builtins
-        Kernel::load File.join(Lexers::BASE_DIR, 'matlab/keywords.rb')
-        builtins
-      end
+      require_relative "matlab/keywords"
 
       state :root do
         rule %r/\s+/m, Text # Whitespace

lib/rouge/lexers/matlab/builtins.rb

@@ -41,11 +41,14 @@ module Rouge
           yield   ""
           yield   "module Rouge"
           yield   "  module Lexers"
-          yield   "    def Matlab.builtins"
-          yield   "      @builtins ||= Set.new #{keywords.inspect}"
+          yield   "    class Matlab"
+          yield   "      def self.builtins"
+          yield   "        @builtins ||= Set.new #{keywords.inspect}"
+          yield   "      end"
           yield   "    end"
           yield   "  end"
           yield   "end"
+          yield   ""
         end
       end
     end