code: function _setIn (source, key, value) {
      var result = {};
  
      for (var prop in source) {
          result[prop] = source[prop];
      }
  
      result[key] = value;
  
      return result;
  }
docs: Sets, or creates, a property in a copy of the provided object to the desired value.
  @private
  @param {Object} source
  @param {String} key
  @param {*} value
  @returns {Object}