Add @dynamic property for UIActivityIndicatorView that solves memory leak issue.
Add @dynamic property for UIActivityIndicatorView that solves memory leak issue.

yuweijie021/UIActivityIndicator-for-SDWebImage,yaoxiaoyong/UIActivityIndicator-for-SDWebImage,takeshineshiro/UIActivityIndicator-for-SDWebImage,JJSaccolo/UIActivityIndicator-for-SDWebImage,basecom/UIActivityIndicator-for-SDWebImage,jrmiddle/UIActivityIndicator-for-SDWebImage,nobre84/UIActivityIndicator-for-SDWebImage,yarec/UIActivityIndicator-for-SDWebImage