麻烦升级nokogirigemv1.5.2，libxml2过时

我试图安装更新版本的nokogiri gem（从1.4.3.1开始到1.5.2）。

我得到的输出如下所示：

[~]# gem install nokogiri -v '1.5.2' Building native extensions. This could take a while... ERROR: Error installing nokogiri: ERROR: Failed to build gem native extension. /path/to/rvm/rubies/ruby-1.8.7-p352/bin/ruby extconf.rb checking for libxml/parser.h... yes checking for libxslt/xslt.h... yes checking for libexslt/exslt.h... yes checking for iconv_open() in iconv.h... yes checking for xmlParseDoc() in -lxml2... yes checking for xsltParseStylesheetDoc() in -lxslt... yes checking for exsltFuncRegister() in -lexslt... yes checking for xmlHasFeature()... no ----- The function 'xmlHasFeature' is missing from your installation of libxml2. Likely this means that your installed version of libxml2 is old enough that nokogiri will not work well. To get around this problem, please upgrade your installati on of libxml2. 

这是一个RPM v4.3.3的RedHat盒子，我假定libxml2需要更新。 它看起来像当前版本是：

MODULE_VERSION = “xml2-2.6.16”

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但是我不熟悉升级命令/过程的样子，你能帮忙吗？