Simple: Patch node.style.animation to work when undefined

[uglow]

In https://github.com/sveltejs/svelte/blob/master/src/shared/transitions.js:

export function generateKeyframes ( a, b, delta, duration, ease, fn, node, style ) {
	var id = '__svelte' + ~~( Math.random() * 1e9 ); // TODO make this more robust
	var keyframes = '@keyframes ' + id + '{\n';

	for ( var p = 0; p <= 1; p += 16.666 / duration ) {
		var t = a + delta * ease( p );
		keyframes += ( p * 100 ) + '%{' + fn( t ) + '}\n';
	}

	keyframes += '100% {' + fn( b ) + '}\n}';
	style.textContent += keyframes;

	document.head.appendChild( style );

	node.style.animation = node.style.animation.split( ',' )    // <----- Change this line
		.filter( function ( anim ) {
			// when introing, discard old animations if there are any
			return anim && ( delta < 0 || !/__svelte/.test( anim ) );
		})
		.concat( id + ' ' + duration + 'ms linear 1 forwards' )
		.join( ', ' );
}

In PhantomJS (which is nearing end-of-life, but some of us still need to use it), the node.style.animation = ... line produces an error (see sveltejs/svelte-transitions#2).

When this line is changed to:

	node.style.animation = (node.style.animation || '').split( ',' )

... PhantomJS runs as expected.

I know this is a PhantomJS bug, but PhantomJS is no longer maintained.

[PaulBGD]

Well, actually any unknown CSS property returns undefined and according to this http://caniuse.com/#feat=css-animation IE<10 doesn't support CSS animations. So this would also be a fix for those browsers.