The default mime type can be set to application/octet-stream rather than text/plain in MimeTypeHelper

[navjot50]

Current implementation of library sets the mime type of a file for which it doesn't know the extension to text/plain. I recently had a situation where I had to upload .msi files to wordpress backend. If a mime type is not explicitly passed as a parameter to Media.Create method then it will set the mime type to text/plain. I think for the unrecognized extensions application/octet-stream is a more correct fit according to: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types