使用框架
https://github.com/mokagio/UICollectionViewLeftAlignedLayout
参考：
UICollectionView 一行cell如何左对齐
https://www.jianshu.com/p/f042944a605d
[iOS]UICollectionView的Cell左对齐
https://blog.csdn.net/wsyx768/article/details/90772223?utm_medium=distribute.pc_feed_404.none-task-blog-BlogCommendFromBaidu-7.nonecase&depth_1-utm_source=distribute.pc_feed_404.none-task-blog-BlogCommendFromBaidu-7.nonecas
UICollectionView Cell大小自适应 并靠左对齐最简单的实现
https://www.jianshu.com/p/485daf52973b
