Update ruby-nokogiri to 1.5.3.

== 1.5.3 / 2012-06-01

* Features

  * Support for "prefixless" CSS selectors ~, > and + like jQuery
    supports. #621, #623. (Thanks, David Lee!)
  * Attempting to improve installation on homebrew 0.9 (with regards
    to iconv). Isn't package management convenient?

* Bugfixes

  * Custom xpath functions with empty nodeset arguments cause a
    segfault. #634.
  * Nokogiri::XML::Node#css now works for XML documents with default
    namespaces when the rule contains attribute selector without
    namespace.
  * Fixed marshalling bugs around how arguments are passed to (and
    returned from) XSLT custom xpath functions. #640.
  * Nokogiri::XML::Reader#outer_xml is broken in JRuby #617
  * Nokogiri::XML::Attribute on JRuby returns a nil namespace #647
  * Nokogiri::XML::Node#namespace= cannot set a namespace without a
    prefix on JRuby #648
  * [JRuby] 1.9 mode causes dead lock while running rake #571
  * HTML::Document#meta_encoding does not raise exception on docs with
    malformed content-type. #655
  * Fixing segfault related to unsupported encodings in in-context
    parsing on 1.8.7. #643
  * [JRuby] Concurrency issue in XPath parsing. #682

(taca)