include a "garble version" test (#221)

Not sure why the last commit came with none.

While at it, I noticed that the version command would ignore arguments.
Error instead.

main.go

@@ -247,10 +247,13 @@ How to install Go: https://golang.org/doc/install
 
 func mainErr(args []string) error {
 	// If we recognize an argument, we're not running within -toolexec.
-	switch cmd := args[0]; cmd {
+	switch cmd, args := args[0], args[1:]; cmd {
 	case "help":
 		return flag.ErrHelp
 	case "version":
+		if len(args) > 0 {
+			return fmt.Errorf("the version command does not take arguments")
+		}
 		// don't overwrite the version if it was set by -ldflags=-X
 		if info, ok := debug.ReadBuildInfo(); ok && version == "(devel)" {
 			mod := &info.Main
@@ -267,7 +270,7 @@ func mainErr(args []string) error {
 		}
 		// Split the flags from the package arguments, since we'll need
 		// to run 'go list' on the same set of packages.
-		flags, args := splitFlagsFromArgs(args[1:])
+		flags, args := splitFlagsFromArgs(args)
 		for _, f := range flags {
 			switch f {
 			case "-h", "-help", "--help":

testdata/scripts/help.txt

@@ -27,3 +27,12 @@ stderr 'unknown command'
 [!windows] ! garble /does/not/exist/compile
 [windows] ! garble C:\does\not\exist\compile
 stderr 'not running "garble \[command\]"'
+
+garble version
+stdout 'devel|^v0'
+
+! garble version -flag
+stderr 'does not take arguments'
+
+! garble version arg
+stderr 'does not take arguments'