v1.0.7

1. fix Strange error

v1.0.6

1. add static method CachedImage.isUrlCached(url,success=(cachFile)=>void,fail=(error)=>void))
2. add static method CachedImage.getCacheFilename(url)
3. add static property CachedImage.cacheDir, user can use to set customized cacheDir

v1.0.5

v1.0.5
fix for RN 0.59+

v1.0.4
fix Content-Length check

v1.0.3

1. fix file successfully download check