hexadecimal: Ensure test versioning consistency with other exercises
hexadecimal: Ensure test versioning consistency with other exercises

* Moved TestTestVersion to top of the testing functions
* Errorf -> Fatalf

See #470

exercism/xgo,exercism/xgo,robphoenix/exercism-go,robphoenix/exercism-go,leenipper/xgo,leenipper/xgo