Add some Content-Types to assetsNotGzipped

[gmetais]

Hi Maciej!

Here are some assets types that could be added to the metric assetsNotGzipped:

• JSON: (entry.isJSON)
• SVG: (entry.contentType === "image/svg+xml")
• TTF: (entry.contentType === "application/x-font-ttf" || entry.contentType === "font/ttf")
• XML: (entry.contentType === ''text/xml" || entry.contentType === "application/xml")
• favicon: (entry.contentType === "image/x-icon" || entry.contentType === "image/vnd.microsoft.icon")

https://github.com/macbre/phantomas/blob/devel/modules/staticAssets/staticAssets.js#L48-L54

Improves 48ab0d1

[gmetais]

👍