Update grep for build date command

.travis.yml

@@ -15,7 +15,7 @@ script:
 - while ! nc -z 127.0.0.1 2222; do echo 'Waiting for Coinboot machine to listen on
  port 2222/SSH ...'; sleep 10; done
 - while ! sshpass -p ubuntu ssh -o StrictHostKeyChecking=no -v -l ubuntu -p 2222 localhost
- grep -C 10 20180906 /etc/motd ; do echo 'Waiting for SSH login to succeed...'; sleep
+ grep -C 10 20180922 /etc/motd ; do echo 'Waiting for SSH login to succeed...'; sleep
  10; done
 after_success:
 - git config --global user.email "[email protected]"