update to use xenial builder for CQ/CI

Change-Id: I858f062fb610690f9f60275f331ecf3daeb9d45c
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/5600
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>

commit-queue.cfg

diff --git a/commit-queue.cfg b/commit-queue.cfg
index 6cef67d..8795619 100644
--- a/commit-queue.cfg
+++ b/commit-queue.cfg
@@ -12,7 +12,7 @@
     url: "https://gn-review.googlesource.com"
     projects {
       name: "gn"
-      ref_regexp: "refs/heads/.+"
+      ref_regexp: "refs/heads/master"
     }
   }
   verifiers {

cr-buildbucket.cfg

diff --git a/cr-buildbucket.cfg b/cr-buildbucket.cfg
index 03d0dc8..43ca908 100644
--- a/cr-buildbucket.cfg
+++ b/cr-buildbucket.cfg
@@ -72,7 +72,7 @@
 
     builders {
       name: "linux"
-      dimensions: "os:Ubuntu-14.04"
+      dimensions: "os:Ubuntu-16.04"
       dimensions: "cpu:x86-64"
     }
 
@@ -114,7 +114,7 @@
 
     builders {
       name: "linux"
-      dimensions: "os:Ubuntu-14.04"
+      dimensions: "os:Ubuntu-16.04"
       dimensions: "cpu:x86-64"
     }