Add weili@ to printing/OWNERS

Change-Id: Ifb231fe7f7b686c417cecc3cad6534239bec5066
Reviewed-on: https://chromium-review.googlesource.com/996315Reviewed-by: Wei Li <weili@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548337}

printing/OWNERS

 dpapad@chromium.org
 rbpotter@chromium.org
 thestig@chromium.org
+weili@chromium.org
 
 per-file printing_context_android*=dgn@chromium.org