Cannot create service with read_only attribute due to missing comma in CONTAINER_SPEC_KWARGS

[jekyc]

Hi,

There seems to be a typo on the following line, which is missing a comma.

docker-py/docker/models/services.py

Line 279 in 22b7b76

'privileges'

The effect of this, is that it is not possible to use the read_only flag for services.

[shin-]

Thanks for the report! Feel free to submit a PR!