Fixes license for setuptools > v56.1.0

I got the following error when trying to install with setuptools==57.0.0

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/tmp/pip-req-build-obm7mx6j/setup.py", line 29, in <module>
    setup(name='pyrle',
  File "/home/mathieu/miniconda3/envs/MC2021-04-22/lib/python3.9/distutils/core.py", line 148, in setup
    dist.run_commands()
  File "/home/mathieu/miniconda3/envs/MC2021-04-22/lib/python3.9/distutils/dist.py", line 966, in run_commands
    self.run_command(cmd)
  File "/home/mathieu/miniconda3/envs/MC2021-04-22/lib/python3.9/distutils/dist.py", line 985, in run_command
    cmd_obj.run()
  File "/home/mathieu/.local/share/virtualenvs/pps-xKT5X8cF/lib/python3.9/site-packages/setuptools/command/egg_info.py", line 292, in run
    writer(self, ep.name, os.path.join(self.egg_info, ep.name))
  File "/home/mathieu/.local/share/virtualenvs/pps-xKT5X8cF/lib/python3.9/site-packages/setuptools/command/egg_info.py", line 635, in write_pkg_info
    metadata.write_pkg_info(cmd.egg_info)
  File "/home/mathieu/miniconda3/envs/MC2021-04-22/lib/python3.9/distutils/dist.py", line 1117, in write_pkg_info
    self.write_pkg_file(pkg_info)
  File "/home/mathieu/.local/share/virtualenvs/pps-xKT5X8cF/lib/python3.9/site-packages/setuptools/dist.py", line 185, in write_pkg_file
    license = rfc822_escape(self.get_license())
  File "/home/mathieu/miniconda3/envs/MC2021-04-22/lib/python3.9/distutils/util.py", line 476, in rfc822_escape
    lines = header.split('\n')
AttributeError: 'list' object has no attribute 'split'

It was fine with setuptools==52.0.0.

I think the change occur in setuptool 56.1.0 : https://github.com/pypa/setuptools/commit/c36033859ec2f7d9034a93c363ffc858ffbae172#diff-b64ef3dbcb447d2cfc0a81bcba734f9f7d58440adcc078fb23a31949b7c723d4

There is a new line checking the license and the license=["MIT"] is now invalid.

pyranges / pyrle

Fixes license for setuptools > v56.1.0 #3