Make test confom to new requirement enforced in go 1.10

[jcajka]

https://tip.golang.org/doc/go1.10#test. With out this change tests will always fails with go 1.10+.

# github.com/spacemonkeygo/openssl
go/src/github.com/spacemonkeygo/openssl/key_test.go:80: Fatal call has possible formatting directive %s
go/src/github.com/spacemonkeygo/openssl/key_test.go:294: Fatal call has possible formatting directive %s
go/src/github.com/spacemonkeygo/openssl/sha1_test.go:38: Fatal call has possible formatting directive %x
go/src/github.com/spacemonkeygo/openssl/sha1_test.go:76: Fatal call has possible formatting directive %x
go/src/github.com/spacemonkeygo/openssl/sha256_test.go:38: Fatal call has possible formatting directive %x
go/src/github.com/spacemonkeygo/openssl/sha256_test.go:76: Fatal call has possible formatting directive %x
FAIL    github.com/spacemonkeygo/openssl [build failed]

[zeebo]

thanks!