[Fix] Panel docker build broken without php7-sodium dependency

[Izumemori]

Due to composer errors not aborting the docker build a faulty image was pushed and renders the panel non-functional.

  Problem 1
    - lcobucci/jwt is locked to version 4.1.4 and an update of this package was not requested.
    - lcobucci/jwt 4.1.4 requires ext-sodium * -> it is missing from your system. Install or enable PHP's sodium extension.

Adding the php7-sodium package solves this and makes composer pull all deps again.

[halkeye]

awesome! I just added #116 which should prevent it hidden breaking in the future.

[ccarney16]

Merged, and starting the build process