Add support for 3mf

[Ugzuzg]

It follows the Open Packaging Conventions, so the detection is very similar to docx or odt.

The 3D Model part name SHOULD contain two segments, the first being "/3D/" and the second with the extension ".model" on the last segment, for example "/3D/3dModel.model".
-- https://github.com/3MFConsortium/spec_core/blob/master/3MF%20Core%20Specification.md#22-part-naming-recommendations

https://www.iana.org/assignments/media-types/model/3mf

[sindresorhus]

Suggested change

	if (zipHeader.filename.startsWith('3D/') && zipHeader.filename.endsWith('.model')) {
	if (zipHeader.filename.startsWith('/3D/') && zipHeader.filename.endsWith('.model')) {

[Ugzuzg]

There's no leading slash in the filenames of any of the zip-based formats. The above will fail.
xlsx has the same implementation: https://github.com/sindresorhus/file-type/blob/master/core.js#L314-L319

[Borewit]

Looks good to me. Another way, to determine the file, would be search for [Content_Types].xml , unzip that file, parse the XML, use the content-types. But not feasible in this context, I think this is the best way indeed.