Replace breaks on keywords within mixin invocations

[SLaks]

Source:

@keyword: test;
.test {
    content: replace(@keyword, '(^[a-z])', '.$1');
}
a {
    .test();
}

Actual Result:

.test {
  content: .test;
}
a {
  content: ..test.;
}

Expected Result:

.test {
  content: .test;
}
a {
  content: .test;
}

Workarounds:
Turning the keyword into a string fixes this: e(replace('@{keyword}', '(^[a-z])', '.$1'))

Also, this only happens if the replace() call is inside a mixin invocation.

[seven-phases-max]

See #2308 (fixed in v2.1.1).

[seven-phases-max]

Closing as fixed with v2.1.1 (#2309).