add xmlns attribute for downloaded SVG

[zehraworks]

Fix #262

[aykutkardas]

Adding a new method increases code duplication.

You can add a new parameter for the existing method instead.

If this parameter exists, attributes that should be in SVG files are added.

export const convertToSVG = ({ icon }: IconSetItem, size = 32, isFile = false) => {...}

// ...

convertToSVG(icon, size, true)