Minor bug fix

http://127.0.0.1:8000/eden/vol/person?group=volunteer&human_resource.id=102
and 
http://127.0.0.1:8000/eden/member/person?membership.id=1
gave error before.

To explain it: according to conventions (PEP8), class names shall be uppercase. However, since the class is defined in a model, we do need the hrm_ prefix to have it available via s3db. Therefore, it is hrm_CV = hrm_ (model prefix) plus CV (uppercase class name).