vup: use v.exe

cmd/tools/vup.v

@@ -66,7 +66,11 @@ fn main() {
 
 fn show_current_v_version(){
 	println('Current V version:')
-	os.system('v version')
+	$if windows {
+		os.system('v.exe version')
+	}	$else {
+		os.system('v version')
+	}
 }
 
 fn backup(file string) {