Received this error when installing nokogiri

nokogiri_error.txt

D:\GitHub\showcases\intellij-sdk-docs>rake bootstrap
bundle install --path sdkdocs-template/_vendor/bundle
Fetching gem metadata from https://rubygems.org/...........
Fetching version metadata from https://rubygems.org/...
Fetching dependency metadata from https://rubygems.org/..
Resolving dependencies...
Using rake 10.4.2
Installing nokogiri 1.5.11 with native extensions

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    C:/tools/ruby21/bin/ruby.exe -r ./siteconf20150716-2584-1bwyvut.rb extconf.r
b
The system cannot find the path specified.
checking for libxml/parser.h... no
-----
libxml2 is missing.  please visit http://nokogiri.org/tutorials/installing_nokog
iri.html for help with installing dependencies.
-----
*** 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=C:/tools/ruby21/bin/ruby
        --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-iconv-dir
        --without-iconv-dir
        --with-iconv-include
        --without-iconv-include=${iconv-dir}/include
        --with-iconv-lib
        --without-iconv-lib=${iconv-dir}/lib
        --with-xml2-dir
        --without-xml2-dir
        --with-xml2-include
        --without-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-libxml-2.0-config
        --without-libxml-2.0-config
        --with-pkg-config
        --without-pkg-config
        --with-libiconv-config
        --without-libiconv-config
        --with-pkg-config
        --without-pkg-config

extconf failed, exit code 1

Gem files will remain installed in D:/GitHub/showcases/intellij-sdk-docs/sdkdocs
-template/_vendor/bundle/ruby/2.1.0/gems/nokogiri-1.5.11 for inspection.
Results logged to D:/GitHub/showcases/intellij-sdk-docs/sdkdocs-template/_vendor
/bundle/ruby/2.1.0/extensions/x64-mingw32/2.1.0/nokogiri-1.5.11/gem_make.out
An error occurred while installing nokogiri (1.5.11), and Bundler cannot
continue.
Make sure that `gem install nokogiri -v '1.5.11'` succeeds before bundling.
rake aborted!
Command failed with status (5): [bundle install --path sdkdocs-template/_ve...]
D:/GitHub/showcases/intellij-sdk-docs/sdkdocs-template/rakelib/sdkdocs.rake:16:i
n `block in <top (required)>'
Tasks: TOP => bootstrap
(See full trace by running task with --trace)