Log Message:
Update ruby-sass to 3.4.23.

3.4.23 (19 December 2016)

* The Sass logger is now instantiated on a per-thread/per-fiber basis and can
  now be configured to output to any IO object. This can help services and
  processes that wrap Sass compilation reliably extract warnings in a
  concurrent environment.

* Setting the numeric precision by assigning to
  Sass::Script::Value::Number.precision is now thread safe. To set for all
  threads, be sure to set the precision on the main thread.

* Sass cache files will now be world and group writable if your umask allows
  it. Issue #1623

* The supports(...) clause in @import statements now allows bare declarations
  as per the CSS specification. Issue #1967

* Fix a bug where, under some circumstances, str-slice() would go to the end
  of the string even if $end-at was set.

* Fix conversions between numbers with dpi, dpcm, and dppx units. Previously
  these conversions were inverted.

* Support url()s containing quoted strings within unknown directives.