Change minimal PIN length to 14

[szszszsz]

Due to a recent hardware attack the short PINs are not safe. To increase the minimal PIN length up to 14, without any additional constraints.

Details:

• https://support.nitrokey.com/t/key-generation-with-nitrokey-start-on-debian-buster-fails-rsa4096/2339/11
• https://support.nitrokey.com/t/key-generation-with-nitrokey-start-on-debian-buster-fails-rsa4096/2339/10

[szszszsz]

Fixed with 2e29ab3