Validations type is too restrictive

[ugostack]

Hello everyone,

If we want to pass some specific validation like a RegExp object, it seems that the type is too restrictive. It supports only a Record of string, Validation where Validation is a string, boolean or a validation function.

https://github.com/formsy/formsy-react/blob/master/src/interfaces.ts#L22

I think that the Validation should support RegExp :)

Thank you in advance,