Fix missing Number.isNaN in IE
Fix missing Number.isNaN in IE

See https://github.com/sourcelair/xterm.js/pull/525#issuecomment-278497452
Tyriar/xterm.js,xtermjs/xterm.js,Tyriar/xterm.js,cjordog/NRLWebsite,akalipetis/xterm.js,akalipetis/xterm.js,cjordog/NRLWebsite,xtermjs/xterm.js,sourcelair/xterm.js,xtermjs/xterm.js,xtermjs/xterm.js,cjordog/NRLWebsite,sourcelair/xterm.js,sourcelair/xterm.js,akalipetis/xterm.js,sourcelair/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js,cjordog/NRLWebsite,Tyriar/xterm.js,Tyriar/xterm.js,Tyriar/xterm.js