gl.lineWidth() is not supported on most modern browsers

It seems like `gl.lineWidth` which is used on [errorsbars.js#L59](https://github.com/gl-vis/gl-error3d/blob/e2fa31bbd3d23526d4e4b165a74ed622ee5a4465/errorbars.js#L59) is deprecated. As a result, we can't change the thickness of error bars.