use bionic repos

sources.list

 # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
 # newer versions of the distribution.
 
-deb http://archive.ubuntu.com/ubuntu/ xenial main restricted
-deb-src http://archive.ubuntu.com/ubuntu/ xenial main restricted
+deb http://archive.ubuntu.com/ubuntu/ bionic main restricted
+deb-src http://archive.ubuntu.com/ubuntu/ bionic main restricted
 
 ## Major bug fix updates produced after the final release of the
 ## distribution.
-deb http://archive.ubuntu.com/ubuntu/ xenial-updates main restricted
-deb-src http://archive.ubuntu.com/ubuntu/ xenial-updates main restricted
+deb http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted
+deb-src http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted
 
 ## Uncomment the following two lines to add software from the 'universe'
 ## repository.
 ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
 ## team. Also, please note that software in universe WILL NOT receive any
 ## review or updates from the Ubuntu security team.
-deb http://archive.ubuntu.com/ubuntu/ xenial universe multiverse
-deb-src http://archive.ubuntu.com/ubuntu/ xenial universe multiverse
-deb http://archive.ubuntu.com/ubuntu/ xenial-updates universe multiverse
-deb-src http://archive.ubuntu.com/ubuntu/ xenial-updates universe multiverse
+deb http://archive.ubuntu.com/ubuntu/ bionic universe multiverse
+deb-src http://archive.ubuntu.com/ubuntu/ bionic universe multiverse
+deb http://archive.ubuntu.com/ubuntu/ bionic-updates universe multiverse
+deb-src http://archive.ubuntu.com/ubuntu/ bionic-updates universe multiverse
 
 ## N.B. software from this repository may not have been tested as
 ## extensively as that contained in the main release, although it includes
 ## newer versions of some applications which may provide useful features.
 ## Also, please note that software in backports WILL NOT receive any review
 ## or updates from the Ubuntu security team.
-# deb http://archive.ubuntu.com/ubuntu/ xenial-backports main restricted
-# deb-src http://archive.ubuntu.com/ubuntu/ xenial-backports main restricted
+# deb http://archive.ubuntu.com/ubuntu/ bionic-backports main restricted
+# deb-src http://archive.ubuntu.com/ubuntu/ bionic-backports main restricted
 
-deb http://archive.ubuntu.com/ubuntu/ xenial-security main restricted
-deb-src http://archive.ubuntu.com/ubuntu/ xenial-security main restricted
-deb http://archive.ubuntu.com/ubuntu/ xenial-security universe multiverse
-deb-src http://archive.ubuntu.com/ubuntu/ xenial-security universe multiverse
+deb http://archive.ubuntu.com/ubuntu/ bionic-security main restricted
+deb-src http://archive.ubuntu.com/ubuntu/ bionic-security main restricted
+deb http://archive.ubuntu.com/ubuntu/ bionic-security universe multiverse
+deb-src http://archive.ubuntu.com/ubuntu/ bionic-security universe multiverse