Add transparency to line

[mmarkelov]

Right now there is no way to use transparency for line:

slide.addShape(pptx.shapes.OVAL_CALLOUT, {
  x: 6,
  y: 2,
  w: 3,
  h: 2,
  fill: { color: "ff0000", transparency: 50 },
  line: { color: "000000", width: 10, transparency: 50 },
});

This PR will fix it

[gitbrent]

Thanks @mmarkelov !