使用佈局時適配UILabel文字

寬度不夠時，可以被壓縮 

[_label setContentCompressionResistancePriority:UILayoutPriorityFittingSizeLevel forAxis:UILayoutConstraintAxisHorizontal];

抱緊 類似於sizeToFit 

[_label setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];

不可以被壓縮，儘量顯示完整 

[_label setContentCompressionResistancePriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];