fix: use ubuntu-latest as ci runner

[UlisesGascon]

No description provided.

[UlisesGascon]

This will require some work. I am not working on this now, so help is more than welcome :)

So far seems like the signatures for [email protected] are not available (ref)

Get:37 http://us.archive.ubuntu.com/ubuntu bionic InRelease [242 kB]
Err:8 http://security.ubuntu.com/ubuntu bionic-security InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32
Err:37 http://us.archive.ubuntu.com/ubuntu bionic InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32
Reading package lists...
W: GPG error: http://security.ubuntu.com/ubuntu bionic-security InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32
E: The repository 'http://security.ubuntu.com/ubuntu bionic-security InRelease' is not signed.
W: GPG error: http://us.archive.ubuntu.com/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32
E: The repository 'http://us.archive.ubuntu.com/ubuntu bionic InRelease' is not signed.
Error: Process completed with exit code 100.

[bjohansebas]

@UlisesGascon expressjs/discussions#236 and jshttp/range-parser#26 (comment) so I'm in favor of removing support for Node 0.6 in the CI

[UlisesGascon]

I will merge this PR while solving the [email protected] in a separate PR.