Update ruby-sass to 3.2.15

3.2.15 (7 March 2014)

* Support &.foo when the parent selector has a newline followed by a comma.

3.2.14 (24 January 2014)

* Don't crash when parsing a directive with no name in the indented syntax.
* Clean up file paths when importing to avoid errors for overlong path names.
* Parse calls to functions named true, false, and null as function calls.
* Don't move CSS @imports to the top of the file unless it's necessary.

3.2.13 (19 December 2013)

* Numbers returned by user-defined functions now trigger division, just like
  numbers stored in variables.
* Support importing files in paths with open brackets.
* Fix sass-convert's handling of rules with empty bodies when converting from
  CSS.
* Fix CSS imports using url() with a quoted string and media queries.

3.2.12 (4 October 2013)

* Add a couple missing requires, fixing some load errors, especially when
  using the command-line interface.
* Tune up some heuristics for eliminating redundant generated selectors. This
  will prevent some selector elimination in cases where multi-layered @extend
  is being used and where it seems intuitively like selectors shouldn't be
  eliminated.

3.2.11 (27 September 2013)

* Fix @extend's semantics with respect to pseudo-elements. They are no longer
  treated identically to pseudo-classes.
* A more understandable error is now provided when the -E option is passed to
  the Sass command line in ruby 1.8
* Fixed a bug in the output of lists containing unary plus or minus operations
  during sass <=> scss conversion.
* Avoid the IE7 content: counter bug with content: counters as well.
* Fix some thread-safety issues.

(taca)