Bug#900182: Proposed fix

[Xavier]

Hi all,

I pushed an MR[1] to fix this CVE tagged as "high" and also
CVE-2018-19827 (medium), CVE-2019-6283 (low), CVE-2019-6284 (low) and
CVE-2019-6286 (low)

Cheers,
Xavier

[1]: https://salsa.debian.org/sass-team/libsass/merge_requests/1