Fix lost this context in resize event handler

[vyobukhov]

Resize function has a broken this context right now. It was not an issue in previous versions because stdout was used directly

this.width = stdout.columns;
this.height = stdout.rows - 1;

And now, when this.stream is used, library crashes on resize

this.width = this.stream.columns;
this.height = this.stream.rows;

[kamiyo]

lgtm. Sorry I overlooked this.