Attempt to fix an issue with split view drawing artifacts on 10.14

Source/SPSplitView.m

@@ -1208,6 +1208,13 @@ - (id)initWithParent:(SPSplitView *)aSplitView
- (void)_animationStep:(NSTimer *)aTimer
{
	[parentSplitView adjustSubviews];

	// this is required on 10.14 in order to have the dividers move properly, because that OS version forces a layer-backed
	// view and at the same time calls -layout much less often than previous OS X versions, resulting in outdated dividers.
	// That is not an issue on older OS X versions where -drawRect: was used.
	if(isOSAtLeast10_7) {
		[parentSplitView setNeedsLayout:YES]; // 10.7+
	}
}

@end