Head over to plex.tv to grab the download link for your OS and do the following:
❯ wget https://downloads.plex.tv/plex-media-server/1.3.4.3285-b46e0ea/plexmediaserver_1.3.4.3285-b46e0ea_amd64.deb
❯ sudo dpkg -i plexmediaserver_1.3.4.3285-b46e0ea_amd64.deb
❯ rm plexmediaserver_1.3.4.3285-b46e0ea_amd64.deb
❯ sudo service plex restart