'num_clients' renamed to 'num_users'

[poznas]

locustio==0.14.6
locust==1.0.2

in the latest versions of locust 'num_clients' has been renamed to 'num_users'

onHatch() method seems unprepared for that and throws NPE:

@myzhan recently fixed it in locust4j

[anhldbk]

@poznas Thank you. This was fixed in code here. Please upgrade to locust-swarm v1.1.4