function listCacheSet(key, value) {
  var data = this.__data__,
      index = assocIndexOf(data, key);

  if (index < 0) {
    ++this.size;
    data.push([key, value]);
  } else {
    data[index][1] = value;
  }
  return this;
}
Sets the list cache `key` to `value`.

@private
@name set
@memberOf ListCache
@param {string} key The key of the value to set.
@param {*} value The value to set.
@returns {Object} Returns the list cache instance.