code: function propsToString() {
      var props = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : {};
      var defaultProps = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {};
  
      var propStr = '';
  
      Object.keys(props).map(function (prop) {
          var propVal = props[prop];
  
          if (prop !== 'children' && propVal !== defaultProps[prop]) {
              propStr += ' ' + prop + '=';
  
              if (typeof propVal === 'string') {
                  propStr += '"' + propVal + '"';
              } else {
                  propStr += '{' + JSON.stringify(propVal) + '}';
              }
          }
      });
  
      return propStr;
  }
docs: Converts an object of props to a string, excluding defaultProps
  @param  {Object} props - an object of React props
  @param  {Object} defaultProps - an object of defaults
  @return {String}