fix fg color for underline
fix fg color for underline

Tyriar/xterm.js,xtermjs/xterm.js,xtermjs/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,Tyriar/xterm.js,sourcelair/xterm.js,sourcelair/xterm.js,sourcelair/xterm.js,sourcelair/xterm.js,xtermjs/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,Tyriar/xterm.js