Add dpranke@google.com to //OWNERS.

I've switched to using my @google.com address for most work,
so adding it to //OWNERS here.

I'm not removing my @chromium.org address yet, just to make
switching over a bit easier.

Change-Id: If8d6ac06a5193eac79bbd32ea9a5524dcf24b1dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2276571Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Dirk Pranke <dpranke@google.com>

OWNERS

@@ -2,6 +2,7 @@ set noparent
 
 apolito@google.com
 dpranke@chromium.org
+dpranke@google.com
 ehmaldonado@chromium.org
 ehmaldonado@google.com
 jochen@chromium.org