Enable pass on non-linux systems

There is nothing linux specific about pass. In particular, I use it in
openbsd.

Signed-off-by: Rafael Ávila de Espíndola <rafael@espindo.la>

Makefile

@@ -27,7 +27,7 @@ secretservice:
 
 pass:
 	mkdir -p bin
-	go build -o bin/docker-credential-pass pass/cmd/main_linux.go
+	go build -o bin/docker-credential-pass pass/cmd/main.go
 
 wincred:
 	mkdir -p bin