Update rectangle.md (issue #9552)

[brianfajardo]

typeError is shown when floating point values are passed to the rectangle object.

For example, BrowserWindow.setBounds(5, 10, 15.5, 20.5) results in typeError

Added a small note in rectangle.md to add clarity.

[zeke]

Looks good to me. One of the Travis builds seems flaky, so I reran it.

[Vegvizer]

Hi guys,
the issue is that the setBounds() can't get a float number, in order to fix it you can use the Math round function:

for example
const yPosition = process.platform === 'darwin' ? y : y - height;
const xPosition = Math.round(x - width/2);
BrowerWindow.setBounds({
x: xPosition ,
y: yPosition,
width,
height,
});

[sampalm]

@Vegvizer Thanks, you saved me a lot of time.