Update the OWNERS for content/zygote.

Some people have left the team; get an up-to-date list of OWNERS.

Bug: None
Change-Id: I209f4d64c09487cc33d14d68c8bc037b9905cdde
Reviewed-on: https://chromium-review.googlesource.com/772084
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516816}

content/zygote/OWNERS

@@ -1,6 +1,7 @@
 jln@chromium.org
-mdempsky@chromium.org
-rickyz@chromium.org
+palmer@chromium.org
+rsesek@chromium.org
+tsepez@chromium.org
 
 # TEAM: security-dev@chromium.org
 # COMPONENT: Internals>Sandbox