function toPath( parts ) {
	var str;
	var i;
	str = '';
	for ( i = 0; i < parts.length; i++ ) {
		str += '[\'' + parts[ i ] + '\']';
	}
	return str;
}
Returns a key path.

@private
@param {(EmptyArray|StringArray)} parts - path segments
@returns {string} key path

@example
var out = toPath( [] );
// returns ''

@example
var out = toPath( [ 'a', 'b' ] );
// returns "['a']['b']"