Update treeherder-client from 3.0.0 to 4.0.0

[edmorley]

Please can you update treeherder-client to the latest release (4.0.0) to pick up changes to which API endpoints are used (the old endpoints will be disabled at some point in the future):

areweslimyet/requirements.txt

Line 6 in 0b23e6a

treeherder-client==3.0.0

areweslimyet/setup.py

Line 26 in 0b23e6a

"treeherder-client>=3.0.0"

The changelog can be found here:
https://bugzilla.mozilla.org/show_bug.cgi?id=1387711#c2

Many thanks!