jsonalchemy: fix SmartJson dumps documentation
jsonalchemy: fix SmartJson dumps documentation

* Update dumps documentation to describe the new introduced
  parameter.

Signed-off-by: Leonardo Rossi <5460ec99b71a72e7693c4088b5c2585e76e1c857@cern.ch>

tiborsimko/invenio,inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio