由于libpng中缺少符号，brew更新失败

Question

我尝试运行brew update，但后来收到以下错误：

$ brew update
dyld: Symbol not found: __cg_png_create_info_struct
  Referenced from: /System/Library/Frameworks/ImageIO.framework/Versions/A/ImageIO
  Expected in: /usr/local/lib/libPng.dylib
 in /System/Library/Frameworks/ImageIO.framework/Versions/A/ImageIO
Error: Failure while executing: git pull -q origin refs/heads/master:refs/remotes/origin/master

我该如何解决这个问题？我使用版本0.9.5的homebrew和我在OS X的10.10.3上。