Update ruby-curses-gem to 1.2.2.

### 1.2.2 / 2017-04-22

New features:

* Add Curses.get_key_modifiers, Curses.return_key_modifiers, and
  Curses.save_key_modifiers.
* Support mswin native build.  Pull request #29 by usa.

### 1.2.1 / 2017-03-27

New features:

* Add touch, untouch, touched?, touch_line, and line_touched?.

Bug fixes:

* Fix Pad#subpad to use subpad(3). (Issue #23)
* Fix build issues on macOS.  Pull requests #24, #25, #26, #27 and #28 by nobu.

(taca)