Repositorios oficiales de Ubuntu 18.04

 Agregar al final los repositorios oficiales de Ubuntu 18.04

$> sudo vim /etc/apt/sources.list
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deb mirror://mirrors.ubuntu.com/mirrors.txt bionic main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt bionic-updates main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt bionic-backports main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt bionic-security main restricted universe multiverse
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$> sudo apt update