Qt 5.13

[Aleix Pol]

Hey,
A newer Qt version is nearing and I thought it could be useful to be
able to test your stuff on it.
I just uploaded it to apol/asdk5.13.

I just tested it still properly builds apks, didn't even test them, so
use with caution.

Was thinking of putting it into a git branch but I'm not sure it's
worth it, it's a matter of using on the Dockerfile the following
values:

ARG QT_VERSION=5.13.0
ARG QT_TAG=5.13

Happy hacking!
Aleix