Use `basestring` for string type testing. Import from `str` in py3.
Use `basestring` for string type testing. Import from `str` in py3.

ocefpaf/compliance-checker,duncombe/compliance-checker,aodn/compliance-checker,petejan/compliance-checker,lukecampbell/compliance-checker,ioos/compliance-checker,DanielJMaher/compliance-checker