Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

    /usr/bin/ruby extconf.rb --use-system-libraries --with-xml2-include=/usr/include/libxml2
checking if the C compiler accepts ... yes
Building nokogiri using system libraries.
checking for xmlParseDoc() in libxml/parser.h... no
checking for xmlParseDoc() in -lxml2... yes
checking for xsltParseStylesheetDoc() in libxslt/xslt.h... no
checking for xsltParseStylesheetDoc() in -lxslt... yes
checking for exsltFuncRegister() in libexslt/exslt.h... no
checking for exsltFuncRegister() in -lexslt... no
checking for exsltFuncRegister() in -llibexslt... no
-----
libexslt is missing.  Please locate mkmf.log to investigate how it is failing.
-----
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/usr/bin/ruby
	--help
	--clean
	--use-system-libraries
	--with-zlib-dir
	--without-zlib-dir
	--with-zlib-include
	--without-zlib-include=${zlib-dir}/include
	--with-zlib-lib
	--without-zlib-lib=${zlib-dir}/lib
	--with-xml2-dir
	--without-xml2-dir
	--with-xml2-include=${xml2-dir}/include
	--with-xml2-lib
	--without-xml2-lib=${xml2-dir}/lib
	--with-xslt-dir
	--without-xslt-dir
	--with-xslt-include
	--without-xslt-include=${xslt-dir}/include
	--with-xslt-lib
	--without-xslt-lib=${xslt-dir}/lib
	--with-libxslt-config
	--without-libxslt-config
	--with-pkg-config
	--without-pkg-config
	--with-exslt-dir
	--without-exslt-dir
	--with-exslt-include
	--without-exslt-include=${exslt-dir}/include
	--with-exslt-lib
	--without-exslt-lib=${exslt-dir}/lib
	--with-libexslt-config
	--without-libexslt-config
	--with-pkg-config
	--without-pkg-config
	--with-xml2lib
	--without-xml2lib
	--with-xsltlib
	--without-xsltlib
	--with-exsltlib
	--without-exsltlib
	--with-libexsltlib
	--without-libexsltlib


Gem files will remain installed in /root/testi/vendor/bundle/ruby/2.0.0/gems/nokogiri-1.6.6.1 for inspection.
Results logged to /root/testi/vendor/bundle/ruby/2.0.0/gems/nokogiri-1.6.6.1/ext/nokogiri/gem_make.out

An error occurred while installing nokogiri (1.6.6.1), and Bundler cannot continue.
Make sure that `gem install nokogiri -v '1.6.6.1'` succeeds before bundling.