should ask for password if ssh public key fails

```
me@host ~/A/r/oskar> checkoutArangoDB 
Cloning into 'ArangoDB'...
Warning: Permanently added 'github.com,192.30.253.112' (RSA) to the list of known hosts.
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
```
