Gruntfile.js

module.exports = function(grunt) {
  grunt.initConfig({
    // (...)
    copy:{
      // (...)
      options: {
        process: function (content) {
          content = content.replace(/<!-- DEVELOPMENT -->\s*.*\s*<!-- END DEVELOPMENT -->/g,'');
          content = content.replace(/<!-- PRODUCTION\s*(.*)\s*END PRODUCTION -->/g, '$1');
          return content;
        },
      },
      // (...)
    },
  });
  // (...)
};