git-gui: Use sh.exe in Cygwin shortcuts
git-gui: Use sh.exe in Cygwin shortcuts

Because we are trying to execute /bin/sh we know it must be a real
Windows executable and thus ends with the standard .exe suffix.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git