OS X升级El Capitan后，git difftool无法打开diffmerge的解决方法

在git项目下执行git difftool，出现如下报错

/Library/Developer/CommandLineTools/usr/libexec/git-core/mergetools/diffmerge: line 121: diffmerge: command not found

解决方法

ln -s /Applications/DiffMerge.app/Contents/Resources/diffmerge.sh /usr/local/bin/diffmerge