title: sudo-apt get update fails because of spotify repository
body: <p>I've been trying to run <code>sudo apt-get update</code> and it keeps spitting out an error that it failed to fetch <code>http://repository.spotify.com/dists/stable/InRelease</code>. The output is as follows:</p>
  
  <pre><code>Hit:1 http://repo.steampowered.com/steam precise InRelease
  Hit:2 http://packages.microsoft.com/repos/vscode stable InRelease
  Hit:3 http://archive.ubuntu.com/ubuntu xenial InRelease
  Get:4 http://repository.spotify.com stable InRelease [3,302 B]
  Hit:5 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
  Hit:6 https://dl.winehq.org/wine-builds/ubuntu xenial InRelease
  Hit:7 http://archive.ubuntu.com/ubuntu xenial-security InRelease
  Err:4 http://repository.spotify.com stable InRelease
    The following signatures couldn't be verified because the public key         
  is not available: NO_PUBKEY A87FF9DF48BF1C90
  Fetched 3,302 B in 1s (2,125 B/s)
  Reading package lists...Done
  W: An error occured during the signature verification. The repository         
  is not updated and the previous index files will be used. GPG error:         
  http://repository.spotify.com stable InRelease: The following     
  signatures couldn't be verified because the public key is not 
  availiable: NO_PUBKEY A87FF9DF48BF1C90
  W:Failed to fetch http://repository.spotify.com/dists/stable/InRelease 
  The following signatures couldn't be verified because the pupblic key 
  is not available: NO_PUBKEY A87FF9DF48BF1C90
  W: Some index files failed to download. They have been ignored, or old     
  ones used instead. `
  </code></pre>
  
  <p>Now is there some way to completely get rid of the spotify repostitory? or update it maybe? I cant figure it out.</p>