Log Message:
Update ruby-mysql2 to 0.4.6.

0.4.6						2017/5/4

New Features

  None.

Bugfixes

* Mysql2::Error: This connection is still waiting for a result, try again once
  you have the result (#772)
* Handle being terminated while reading query result (#811 )
* Fix segfault on SIGINT race condition (#816, #813)
* Better error messages when the connection options have errors (#831)

Changes

* Use bool instead of my_bool which has been removed since MySQL 8.0.1 (#840,
  #838)
* Reminder for Mac users to install xcode-select (#832)
* Update Travis CI and AppVeyor matrix (#820, #819, #812)
* Update Travis CI for MySQL 8.0 tests (#818, #817)