`get_operation_details` should return a dict keyed by integer IDs

[bdpedigo]

Basically same issue as CAVEconnectome/PCGL2Cache#26 -

If I do

from caveclient import CAVEclient

client = CAVEclient("minnie65_phase3_v1")

root_id = 864691135639556411

client.chunkedgraph.get_operation_details([74531])

the output is

{'74531': {'added_edges': [[89385966883691061, 89385966883698825]],
  'roots': [864691135730164153],
  'sink_coords': [[89384, 96304, 21583]],
  'source_coords': [[89360, 96280, 21577]],
  'timestamp': '2020-08-01 13:07:22.739000+00:00',
  'user': '161'},

i.e. is a dict keyed by strings instead of ints