Fix wrong key name in PublicKeyCredentialCreationOptionsFactory.php, rename authenticator_attachment to attachment_mode

[nicodemuz]

Target branch: 4.7

• [X] It is a Bug fix
• [ ] It is a New feature
• [ ] Breaks BC
• [ ] Includes Deprecations

No idea if this is the correct way to fix this, but when I was upgrading to the latest 4.7 version, I was encountering this issue:

{"status":"error","errorMessage":"Warning: Undefined array key \u0022authenticator_attachment\u0022"}

[Spomky]

This should de fixed by #467

[nicodemuz]

Ah sorry, I didn't see that. I just upgraded to 4.7.x-dev and it seems to work. Thanks!