foliavalidator gives non informative error message when the version attribute is missing

[kosloot]

When validating a document without a version attribute, I get:

Error on line 0: Element FoLiA failed to validate attributes
VALIDATION ERROR against RelaxNG schema (stage 1/3), in tests/GRR.xml
Element FoLiA failed to validate attributes

A more helpful message would include a reference to the missing attribute