Update Crostini release version and channel.

We want to release to dev/canary for version 67 and 68 and to release to
all chanels since version 69.

The beta/stable release is pushed back from 68 to 69.
BUG=chromium:800120
TEST=manual test.

Change-Id: I02851521a0b9266157be3c4eb510546637b538a1
Reviewed-on: https://chromium-review.googlesource.com/1100539Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Tim Zheng <timzheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567321}

chrome/browser/chromeos/virtual_machines/virtual_machines_util.cc

@@ -22,14 +22,15 @@ bool AreVirtualMachinesAllowedByPolicy() {
   return true;
 }
 
-// Disabled for beta/stable channel for M67 and all versions older than M67.
+// Disabled for beta/stable channel for M67 and M68
+// and all versions older than M67.
 bool AreVirtualMachinesAllowedByVersionAndChannel() {
   const base::Version& current_version = version_info::GetVersion();
   if (!current_version.IsValid())
     return false;
   if (current_version.CompareToWildcardString("67.*") < 0)
     return false;
-  if (current_version.CompareToWildcardString("67.*") == 0) {
+  if (current_version.CompareToWildcardString("68.*") <= 0) {
     version_info::Channel channel = chrome::GetChannel();
     return channel != version_info::Channel::STABLE &&
            channel != version_info::Channel::BETA;