Ruby on Rails mysql２が入らない

# Ruby on Rails mysql2 が入らない

bundle installで下記エラー



```
->> bundle install
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
Fetching gem metadata from https://rubygems.org/.........
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies......
Using rake 12.3.0
Using concurrent-ruby 1.0.5
Using i18n 0.9.1
Using minitest 5.11.1
Using thread_safe 0.3.6
Using tzinfo 1.2.4
Using activesupport 5.1.4
Using builder 3.2.3
Using erubi 1.7.0
Using mini_portile2 2.3.0
Using nokogiri 1.8.1
Using rails-dom-testing 2.0.3
Using crass 1.0.3
Using loofah 2.1.1
Using rails-html-sanitizer 1.0.3
Using actionview 5.1.4
Using rack 2.0.3
Using rack-test 0.8.2
Using actionpack 5.1.4
Using nio4r 2.2.0
Using websocket-extensions 0.1.3
Using websocket-driver 0.6.5
Using actioncable 5.1.4
Using globalid 0.4.1
Using activejob 5.1.4
Using mini_mime 1.0.0
Using mail 2.7.0
Using actionmailer 5.1.4
Using activemodel 5.1.4
Using arel 8.0.0
Using activerecord 5.1.4
Using public_suffix 3.0.1
Using addressable 2.5.2
Using bindex 0.5.0
Using bundler 1.16.1
Using byebug 9.1.0
Using xpath 3.0.0
Using capybara 2.17.0
Using ffi 1.9.18
Using childprocess 0.8.0
Using coffee-script-source 1.12.2
Using execjs 2.7.0
Using coffee-script 2.4.1
Using method_source 0.9.0
Using thor 0.20.0
Using railties 5.1.4
Using coffee-rails 4.2.2
Using multi_json 1.13.1
Using jbuilder 2.7.0
Using rb-fsevent 0.10.2
Using rb-inotify 0.9.10
Using listen 3.1.1
Fetching mysql2 0.4.10


Your user account isn't allowed to install to the system RubyGems.
  You can cancel this installation and run:

      bundle install --path vendor/bundle

  to install the gems into ./vendor/bundle/, or you can enter your password
  and install the bundled gems to RubyGems using sudo.

  Password: 


Your user account isn't allowed to install to the system RubyGems.
  You can cancel this installation and run:

      bundle install --path vendor/bundle

  to install the gems into ./vendor/bundle/, or you can enter your password
  and install the bundled gems to RubyGems using sudo.

  Password: 
Installing mysql2 0.4.10 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    /usr/local/rbenv/versions/2.2.2/bin/ruby -r ./siteconf20180113-32465-dhua8u.rb extconf.rb
checking for rb_absint_size()... yes
checking for rb_absint_singlebit_p()... yes
checking for ruby/thread.h... yes
checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
checking for rb_thread_blocking_region()... no
checking for rb_wait_for_single_fd()... yes
checking for rb_hash_dup()... yes
checking for rb_intern3()... yes
checking for rb_big_cmp()... yes
checking for mysql_query() in -lmysqlclient... no
-----
mysql client is missing. You may need to 'apt-get install libmysqlclient-dev' or 'yum install mysql-devel', and try
again.
-----
*** 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/local/rbenv/versions/2.2.2/bin/$(RUBY_BASE_NAME)
	--with-mysql-dir
	--without-mysql-dir
	--with-mysql-include
	--without-mysql-include=${mysql-dir}/include
	--with-mysql-lib
	--without-mysql-lib=${mysql-dir}/lib
	--with-mysql-config
	--without-mysql-config
	--with-mysql-dir
	--without-mysql-dir
	--with-mysql-include
	--without-mysql-include=${mysql-dir}/include
	--with-mysql-lib
	--without-mysql-lib=${mysql-dir}/lib
	--with-mysqlclientlib
	--without-mysqlclientlib

extconf failed, exit code 1

Gem files will remain installed in /tmp/bundler20180113-32465-6bzbzfmysql2-0.4.10/gems/mysql2-0.4.10 for inspection.
Results logged to
/tmp/bundler20180113-32465-6bzbzfmysql2-0.4.10/extensions/x86_64-linux/2.2.0-static/mysql2-0.4.10/gem_make.out

An error occurred while installing mysql2 (0.4.10), and Bundler cannot continue.
Make sure that `gem install mysql2 -v '0.4.10'` succeeds before bundling.

In Gemfile:
  mysql2

```

と出力、真ん中らへんに下記みたいに出力されてる。😲

```
-----
mysql client is missing. You may need to 'apt-get install libmysqlclient-dev' or 'yum install mysql-devel', and try
again.
-----
```
😲

環境: Linux centos 6

足りない、なので下記実行

```
sudo yum install mysql-devel

```

とすると成功します。