Update itext_key_behavior.mixin.js

Some characters don't work in Mac OS X such as dot ".", opened parenthesis "(" and others. The key events return key codes witch are in _keysmap variable and so those characters are not rendered. Ex : '.' event key code return 46.
Merge pull request #1573 from brexis/patch-1

Update itext_key_behavior.mixin.js