Move to mozlog v4.2 for WPT to support known_intermittent statuses.

Bug: 937369
Change-Id: Ief48c90e41affaf469ef80a9e2fd2e86c8f29ba4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1731909
Auto-Submit: Luke Z <lpz@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684136}

.vpython

@@ -322,7 +322,7 @@ wheel: <
 >
 wheel: <
   name: "infra/python/wheels/mozlog-py2_py3"
-  version: "version:4.1"
+  version: "version:4.2.0"
 >
 wheel: <
   name: "infra/python/wheels/mozprocess-py2_py3"