fix printf issues spotted by the latest go vet

main.go

@@ -112,7 +112,7 @@ func (f *seedFlag) Set(s string) error {
 }
 
 func usage() {
-	fmt.Fprintf(os.Stderr, `
+	fmt.Fprint(os.Stderr, `
 Garble obfuscates Go code by wrapping the Go toolchain.
 
 	garble [garble flags] command [go flags] [go arguments]
@@ -139,7 +139,7 @@ garble accepts the following flags before a command:
 
 `[1:])
 	flagSet.PrintDefaults()
-	fmt.Fprintf(os.Stderr, `
+	fmt.Fprint(os.Stderr, `
 
 For more information, see https://github.com/burrowers/garble.
 `[1:])

reverse.go

@@ -18,7 +18,7 @@ import (
 func commandReverse(args []string) error {
 	flags, args := splitFlagsFromArgs(args)
 	if hasHelpFlag(flags) || len(args) == 0 {
-		fmt.Fprintf(os.Stderr, `
+		fmt.Fprint(os.Stderr, `
 usage: garble [garble flags] reverse [build flags] package [files]
 
 For example, after building an obfuscated program as follows: