Explicit 'int' type for keyboard rate defaults

Fixes `KeyRepeat` and `InitialKeyRepeat` for Mavericks.  If unspecified, `defaults write` uses type 'string'. These values should be integers, otherwise they are disregarded.

Note: `boxen::osx_defaults` *will not run* if the new default only differs by type. I'm about to fix that. In the meantime, if you already include `osx::global::key_repeat_rate` and `osx::global::key_repeat_delay` you can test this change with:

    defaults delete -g KeyRepeat
    defaults delete -g InitialKeyRepeat
    boxen
    defaults read-type -g KeyRepeat
    defaults read-type -g InitialKeyRepeat