client can't handle redirect of absolute paths

[Ben Avrahami]

when starlette returns a redirect response (such as when attempting to fix trailing slashes), it returns an absolute path, but async-asgi-testclient always interprets it as a relative path.
I propose that whenever the testclient recieves a redirect, it strip the hostname off the location, if any are found.

[Ben Avrahami]

closed by #53