Fix gerrit_client py3 incompatibility

R=gavinmak@google.com

Bug: 1255669
Change-Id: I4fbbe9fb716a6abd58f40c9ca489a0043ee3584b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3214208Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>

gerrit_client.py

@@ -371,7 +371,7 @@ def CMDmass_abandon(parser, args):
     logging.warn("[ID: %d] %s" % (change['_number'], change['subject']))
 
   if not opt.force:
-    q = raw_input(
+    q = input(
         'Do you want to move forward with abandoning? [y to confirm] ').strip()
     if q not in ['y', 'Y']:
       logging.warn("Aborting...")