Add test for `:not(&-c)`
Add test for `:not(&-c)`

Refs https://github.com/sass/libsass/issues/2630

sass/sass-spec,nschonni/sass-spec,mgreter/sass-spec,sass/sass-spec,sass/sass-spec,nschonni/sass-spec,mgreter/sass-spec,sass/sass-spec,nschonni/sass-spec,mgreter/sass-spec,nschonni/sass-spec