Fix the didStartSwiping delegate selector

The didStartSwiping delegate is never returned due to the selector method missing the colon.

if ([self.delegate respondsToSelector:@selector(swipeTableViewCellDidStartSwiping:)]) {
            [self.delegate swipeTableViewCellDidStartSwiping:self];
}

I added the colon to swipeTableViewCellDidStartSwiping and the delegate methods respond correctly.