Default account is not preserved

[dolmen]

When we run again github-keygen after a default account has been previously selected (--default) the default is not preserved.

How to reproduce:

$ github-keygen dolmen -d
$ github-keygen

Expected output:

Accounts: dolmen
No changes in ~/.ssh/known_hosts_github.
No changes in ~/.ssh/config.

Note: This is a minor issue as the default account can easily be selected again:

$ github-keygen dolmen -d