Add argon2

[eloo]

Hi,
would you mind to add argon2 support to your nginx-php image?
This will be used in nextcloud for password hashing.
If you want i can also provide a PR. (see Wonderfall/docker-nginx-php#4)

Thanks

[hoellen]

Hello,

I added argon2 support with cf3b8c5. The builds are already updated. Thanks for the hint.

With PHP 7.4 there is no need for the additional dependencies (argon2-dev and argon2-libs). So maybe we should remove the package in near future again.

hoellen