Negative variables are not compiled after update

[sn3p]

Did something change regarding the compilation of negative variables?

In v0.14.0 this:

.foo {
  --width: 100px;
  with: -var(--width);
}

used to output:

.foo {
  with: -100px;
}

But after updating to v0.17.0 I get:

.foo {
  with: -var(--width);
}

I tried reproducing in the playground, but this still runs on v0.14.0.

[MadLittleMods]

Looking at the changelog, this probably broke in v0.15.0 where there were some changes around the regex and balanced matching.

Here is the relevant PR #112

cc @Poetro