90% test coverage

[typerandom]

We should aim at having the most important things covered by our tests.

ok      github.com/typerandom/validator             0.007s  coverage: 76.9% of statements
ok      github.com/typerandom/validator/core        0.006s  coverage: 50.8% of statements
ok      github.com/typerandom/validator/core/parser 0.007s  coverage: 90.3% of statements
ok      github.com/typerandom/validator/validators  0.007s  coverage: 70.6% of statements