D:\Windows\system32>gem install releasy
Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
ERROR:  Error installing releasy:
        ERROR: Failed to build gem native extension.

    D:/RailsInstaller/Ruby2.1.0/bin/ruby.exe extconf.rb
checking for socket() in -lsocket... no
checking for gethostbyname() in -lnsl... no
checking for atan() in -lm... yes
checking for inflate() in -lz... no
checking for inflate() in -lzlib... no
checking for inflate() in -lzlib1... no
checking for inflate() in -llibz... no
*** 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=D:/RailsInstaller/Ruby2.1.0/bin/ruby
        --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-zlib-dir
        --without-zlib-dir
        --with-zlib-include
        --without-zlib-include=${zlib-dir}/include
        --with-zlib-lib
        --without-zlib-lib=${zlib-dir}/lib
        --with-socketlib
        --without-socketlib
        --with-nsllib
        --without-nsllib
        --with-mlib
        --without-mlib
        --with-zlib
        --without-zlib
        --with-zliblib
        --without-zliblib
        --with-zlib1lib
        --without-zlib1lib
        --with-libzlib
        --without-libzlib
 extconf failure: need zlib

extconf failed, exit code 1

Gem files will remain installed in D:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1
.0/gems/libxml-ruby-2.8.0 for inspection.
Results logged to D:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/extensions/x86
-mingw32/2.1.0/libxml-ruby-2.8.0/gem_make.out

D:\Windows\system32>