code: function (srcPath, options) {
          _.defaults(options || (options = {}), DEFAULT_OPTIONS);
          var separator = options.separator;
          var extname = path.extname(srcPath);
          var reg = new RegExp('^.+' + separator + '(.+)((' + separator + '.+)|(@\\d+x))\\' + extname + '$');
          if (extname === '.styl' || extname === '.css') {
              reg = new RegExp('^.+' + separator + '(.+)\\' + extname + '$');
          }
          var result = path.basename(srcPath).match(reg);
          return result && result[1];
      }
docs: getGroup
  @param {String} srcPath
  @param {Object} options
  @returns {String}
  @example
  var srcPath = './test/image/sprite/sprite-logo@10x.png';
  var out = getGroup(srcPath);
  console.log(out);
  > 'logo'