math/wxmaxima: Update to 19.05.7

While I'm here:

• Add location to license file

Changelog:

• Support ":lisp" as the first command of the worksheet, in case that maxima is new enough to support that.

https://github.com/wxMaxima-developers/wxmaxima/blob/Version-19.05.7/ChangeLog

PR: 238240
Submitted by: Lorenzo Salvadore <phascolarctos@protonmail.ch> (maintainer)