Allow less-loader v9

[bobvandevijver]

I'm not sure what the policy on node compatibility is, but the latest major of less-loader only seems to drop Node 10 support (release notes).

Webpack Encore still supports Node 10, but that should still be possible if you use one of the other allowed less loaders.

[weaverryan]

You're correct - there's no problem with allowing less-loader 9, as we still allow versions that support Node 10.

However, it's definitely made a mess for the tests. I've just pushed what will hopefully be a workaround.

[bobvandevijver]

Well, Node 10 is no longer supported since the beginning of this month, so we could consider dropping support for it altogether if that makes it easier 😀

[weaverryan]

I’m concerned about ubuntu 20.04 LTS, which I believe comes with node 10. And to bump to 12 just for this reason would be unfortunate :)

[weaverryan]

Plus, I think my last commit fixed things. Appveyor is broken still, but I’m not sure we need to anymore, as we have windows tested by GH actions.

[bobvandevijver]

@weaverryan Is there anything left to do for me before this can be merged and released?

[weaverryan]

Thank you Bob!