Delete trailing whitespace in the readme file

[simleo]

This PR contains minimal changes. Its main purpose is actually to see if the socket.gaierror reported on the Mac instances in #173 is actually unrelated to code changes.

[simleo]

The failing test is test_ftp_uri. The error is triggered by this line:

ro-crate-py/rocrate/model/file.py

Line 50 in 0b375c7

with urllib.request.urlopen(self.source) as response:

Leading to:

socket.gaierror: [Errno 8] nodename nor servname provided, or not known

The test used to pass, so GitHub has probably recently changed the OS of its Mac instances to a version where FTP opening is somehow broken.