Add steveanton to modules/peerconnection OWNERS

Bug: None
Change-Id: I39361bdfe70f51804cdc01e54d474fe064e1b366
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/c/1335888Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Steve Anton <steveanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607994}

third_party/blink/renderer/modules/peerconnection/OWNERS

 guidou@chromium.org
 hbos@chromium.org
 orphis@chromium.org
+steveanton@chromium.org
 tommi@chromium.org
 
 # COMPONENT: Blink>WebRTC