fix bug when css nesting is disabled

[tbela99]

CSS

table.colortable td.c {
 text-transform:uppercase;
}
table.colortable td:first-child, table.colortable td:first-child+td {
 border:1px solid black;
}

JS

const result: TransformResult = await transform(css, {
    beautify: true,
    nestingRules: false
});

Result

table.colortable td.c {
 text-transform: uppercase
}
table,table+td {
 border: 1px solid #000
}

expected

table.colortable td.c {
 text-transform: uppercase
}
table.colortable td:first-child,table.colortable td:first-child+td {
 border: 1px solid #000
}