Incorrect using reference was fixed

Hello. I'm started using easeljs and modified one of your examples. In particular case (with stroke = 1 and green color on white background) line looks less smoothly than in my variant. This is not a problem in your example because you have really thick pen, but you may fix it. You incorrectly initialized object with a reference instead of creating an object.
You may replace 
oldPt = new createjs.Point(stage.mouseX, stage.mouseY);
oldMidPt = oldPt;
with
oldPt = new createjs.Point(stage.mouseX, stage.mouseY);
oldMidPt = new createjs.Point(oldPt.x, oldPt.y);

You can modify handleMouseMove by adding console.log("oldMidPt are equals oldPt: " + (oldMidPt === oldPt)) as here and you'll see the problem:

function handleMouseMove(event) {
            var midPt = new createjs.Point(oldPt.x + stage.mouseX>>1, oldPt.y+stage.mouseY>>1);

            drawingCanvas.graphics.clear().setStrokeStyle(stroke, 'round', 'round').beginStroke(color).moveTo(midPt.x, midPt.y).curveTo(oldPt.x, oldPt.y, oldMidPt.x, oldMidPt.y);

            oldPt.x = stage.mouseX;
            oldPt.y = stage.mouseY;

            oldMidPt.x = midPt.x;
            oldMidPt.y = midPt.y;

            console.log("oldMidPt are equals oldPt: " + (oldMidPt === oldPt));

            stage.update();
        }