From Apple:
When your application is approved by Apple to sell on the App Store, it is encrypted for DRM purposes and re-compressed. When the encryption is added, the size of the compressed file will increase. The exact size of the increase will vary from app to app, however, the size increase can be large when the binary contains a lot of contiguous zeros. We are unable to guarantee the size of your file after the encryption has been added.

苹果会对软件包进行重新加密与压缩，

暂时没有具体的解决办法，

http://stackoverflow.com/questions/5264449/why-is-my-app-5mb-larger-on-the-app-store
这里面推测了为什么会变大

http://www.youxituoluo.com/95823.html
这里面提到bitcode 和使用Xcode6 好像可以解决，（没有实际操作）