Add support for GLB

[eyexpo-thomas]

GLB files are compressed GLTF files.
Website:
https://github.com/KhronosGroup/glTF
Detection information (magic number, header, content, body, etc):
https://github.com/KhronosGroup/glTF/tree/master/extensions/1.0/Khronos/KHR_binary_glTF

If you're adding support for a new file type, please follow the below steps:

[x] Add a fixture file named fixture.<extension> to the fixture directory.
[x] Add the file extension to the types array in test.js.
[x] Add the file type detection logic to the index.js file.
[x] Add the file extension to the Supported file types section in the readme, in the format - [`<extension>`](URL) - Format name, for example, - [`png`](https://en.wikipedia.org/wiki/Portable_Network_Graphics) - Portable Network Graphics
[x] Add the file extension to the keywords array in the package.json file.
[x] Run $ npm test to ensure the tests pass.
[x] Open a pull request with a little like Add support for Format, for example, Add support for PNG.
[x] The pull request description should include a link to the official page of the file format or some other source. Also include a link to where you found the file type detection / magic bytes.

[sindresorhus]

See KhronosGroup/glTF#943

[eyexpo-thomas]

See KhronosGroup/glTF#943

I was going by the output of my WSL Ubuntu's file package, which I suppose is actually wrong.