function labelTransform( orient ) {
	if ( orient === 'bottom' || orient === 'top' ) {
		return 'rotate(0)';
	}
	if ( orient === 'left' ) {
		return 'rotate(-90)';
	}
	// orient === 'right'
	return 'rotate(90)';
}
Returns a label SVG transform.

@private
@param {string} orient - axis orientation
@returns {string} SVG transform