Log Message:
libsass: updated to 3.5.5

3.5.5 Vroom vroom:

Breaking
Revert changes to raw CSS @imports

Deprecations
Add deprecation messages for colour arithmetic

Features
Support hex colors with alpha channels
Add a sass_option_push_import_extension C-API

Fixes
Fix segfault in handling modulo operator
Fix handling of unclosed interpolant in url
Fix possible bug with handling empty reference combinators
Fix -Wmissing-declarations for gcc < 7