function toKey(value) {
  if (typeof value == 'string' || isSymbol(value)) {
    return value;
  }
  var result = (value + '');
  return (result == '0' && (1 / value) == -INFINITY) ? '-0' : result;
}
Converts `value` to a string key if it's not a string or symbol.

@private
@param {*} value The value to inspect.
@returns {string|symbol} Returns the key.