mysql is not part of the bundle,add it to gemfile

连接mysql数据库的时候要注意:
1.用 rails new blog -d mysql 建项目
2.database.yml中，冒号后加空格
3.如果遇到This gem was compiled for 6.0.0 but the client library is 5.x.x
则去download mysql-connector-c-noinstall-6.0.2-win32.zip
下载后 解压把lib目录里的 libmysql.dll复制到 ruby/bin目录