Add GD extension

[dereckson]

The add of pragmarx/google2fa dependency requires the GD extension in PHP to print QR code.

Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - pragmarx/google2fa v0.7.0 requires simplesoftwareio/simple-qrcode 1.3.* -> satisfiable by simplesoftwareio/simple-qrcode[1.3.0, 1.3.1].
    - pragmarx/google2fa v0.7.1 requires simplesoftwareio/simple-qrcode 1.3.* -> satisfiable by simplesoftwareio/simple-qrcode[1.3.0, 1.3.1].
    - simplesoftwareio/simple-qrcode 1.3.1 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - simplesoftwareio/simple-qrcode 1.3.0 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - Installation request for pragmarx/google2fa ^0.7 -> satisfiable by pragmarx/google2fa[v0.7.0, v0.7.1].

[djdefi]

Will try to get to this week. Started a new job at GitHub so been a bit busy with on boarding :)

[djdefi]

GD has been added to base image utilized in versions 2.0+

:latest has GD as well for those bleeding-edge people.