Fix the following format string issue reported by go vet: blake2s_test.go:188: Fatalf format %v reads arg #3, but call has only 2 args Change-Id: I689eadb7d7310ae93acd8a8419755f2724ff41dd Reviewed-on: https://go-review.googlesource.com/75978 Reviewed-by: Filippo Valsorda <hi@filippo.io>