Bug 1526577 [wpt PR 15229] - Update mozlog to 4.0, a=testonly

Automatic update from web-platform-tests
Update mozlog from 3.10 to 4.0 (#15229)

--

wpt-commits: 0e9f46eaa87987da9ee058ea8f511f395ebaf7ec
wpt-pr: 15229

testing/web-platform/tests/tools/wptrunner/requirements.txt

@@ -1,5 +1,5 @@
 html5lib == 1.0.1
 mozinfo == 0.10
-mozlog==3.10
+mozlog==4.0
 mozdebug==0.1.1
 urllib3[secure]==1.24.1