updated mysql2 gem version to 0.4.5.
updated mysql2 gem version to 0.4.5.

smalruby/smalruby-editor,takaokouji/smalruby-editor,takaokouji/smalruby-editor,smalruby/smalruby-editor,takaokouji/smalruby-editor,smalruby/smalruby-editor