Update version specifier

[fabaff]

https://github.com/Paperspace/gradient-cli/blob/9eb645ec208c5cc2c494682705a14602b70f7914/setup.py#L70

is no longer a valid version specifier.

error in gradient setup command: 'install_requires' must be a string or list of strings containing valid project/version requirement specifiers; Expected end or semicolon (after version specifier)
    PyYAML>=5.*
          ~~~^

Affects also websocket-client==0.57.*