Update url

iOS/SDK/README.md

 # Player SDK （iOS）
 
 ## 下载地址
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-[下载 iOS Player SDK](https://liteavsdk-1252463788.cos.ap-guangzhou.myqcloud.com/TXLiteAVSDK_Player_iOS_latest.zip)
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+[下载 iOS Player SDK](https://liteav.sdk.qcloud.com/download/latest/TXLiteAVSDK_Player_iOS_latest.zip)
 
 > Demo 编译时会自动下载SDK到此目录。