Client implementation overly restrictive on HEAD requests

[aspaseltiner-vimeo]

Note: Please report any security issues directly to hello [at] ankit.pl

Describe the bug
sendHeadRequest implementation in the Client only expects a 200-level status. The spec says a server SHOULD return 200 or 204, so the client should probably at least allow 204 statuses.

To Reproduce
Use the client to connect to a Tus server that returns a 204 status code on HEAD requests.

Expected behavior
Head request is treated according to the specification and uploading continues as expected.

I've prepared #454 as a fix.