updated exception syntax for python3

docs/user_docs/source/auth.rst

docs/user_docs/source/lvem.rst

docs/user_docs/source/rest.rst

gracedb/api/v1/events/views.py

gracedb/api/v1/main/views.py

gracedb/core/vfile.py

gracedb/events/serialize.py

gracedb/events/translator.py

gracedb/events/view_logic.py

gracedb/events/views.py

gracedb/search/fields.py