Fixes this:
$ nix-env -f . -qa '*' --meta --xml --drv-path --show-trace
error: while evaluating ‘callPackageWith’ at .../lib/customisation.nix:93:35, called from .../pkgs/top-level/all-packages.nix:1411:24:
while evaluating ‘makeOverridable’ at .../lib/customisation.nix:54:24, called from .../lib/customisation.nix:97:8:
undefined variable ‘srcFC’ at .../pkgs/development/compilers/emscripten-fastcomp/default.nix:26:14
Also, "matthewbauer" is not defined in ./lib/maintainers.nix, comment
out.
Caused by f646b9295ea7a2332667f5ffeb5bd871e76982e9 and
d078fe1e9c826a63ad078ca4d5364c967984f393.
Just use "fetchFromGitHub" because that seems to be more
reliable. Still unclear what the actual issue was but
I'm thinking this will fix it. At least, this will
put it more in line with other packages.