completion: bash: cleanup cygwin check

Avoid Yoda conditions, and use $OSTYPE.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -3499,6 +3499,6 @@ __git_complete gitk __gitk_main
 # when the user has tab-completed the executable name and consequently
 # included the '.exe' suffix.
 #
-if [ Cygwin = "$(uname -o 2>/dev/null)" ]; then
-__git_complete git.exe __git_main
+if [ "$OSTYPE" = cygwin ]; then
+	__git_complete git.exe __git_main
 fi