Merge pull request #319 from chris18890/update-ubuntu

Update ubuntu.ipxe

src/ubuntu.ipxe

@@ -10,10 +10,10 @@ set os Ubuntu
 clear ubuntu_version
 menu ${os} - ${arch_a} - Image Sig Checks: [${img_sigs_enabled}]
 item --gap Latest Releases
+item disco ${space} ${os} 19.04 Disco Dingo
 item cosmic ${space} ${os} 18.10 Cosmic Cuttlefish
 item bionic ${space} ${os} 18.04 LTS Bionic Beaver
 item xenial ${space} ${os} 16.04 LTS Xenial Xerus
-item trusty ${space} ${os} 14.04 LTS Trusty Tahr
 item --gap Older Releases
 item older_release ${space} Set release codename...
 choose ubuntu_version || goto ubuntu_exit