Fix syntax warning in docstring

Sorry for the delay on this, been a while since I've had time to dedicate to this. It seems the python3.7 build is failing consistently -
$ pip install -e .

Obtaining file:///home/travis/build/AntonKueltz/fastecdsa

  Preparing metadata (setup.py) ... error

  error: subprocess-exited-with-error

  × python setup.py egg_info did not run successfully.

  │ exit code: 1

  ╰─> [25 lines of output]

      /home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/setuptools/_importlib.py:23: UserWarning: `importlib-metadata` version is incompatible with `setuptools`.

      This problem is likely to be solved by installing an updated version of `importlib-metadata`.

        warnings.warn(msg)  # Ensure a descriptive message is shown.

      Traceback (most recent call last):

        File "<string>", line 36, in <module>

        File "<pip-setuptools-caller>", line 14, in <module>

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/setuptools/__init__.py", line 18, in <module>

          from setuptools.dist import Distribution

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/setuptools/dist.py", line 34, in <module>

          from ._importlib import metadata

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/setuptools/_importlib.py", line 39, in <module>

          disable_importlib_metadata_finder(metadata)

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/setuptools/_importlib.py", line 12, in disable_importlib_metadata_finder

          import importlib_metadata

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/importlib_metadata/__init__.py", line 471, in <module>

          __version__ = version(__name__)

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/importlib_metadata/__init__.py", line 438, in version

          return distribution(package).version

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/importlib_metadata/__init__.py", line 411, in distribution

          return Distribution.from_name(package)

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/importlib_metadata/__init__.py", line 179, in from_name

          dists = resolver(name)

        File "/home/travis/virtualenv/python3.7.1/lib/python3.7/site-packages/setuptools/_vendor/importlib_metadata/__init__.py", line 886, in find_distributions

          found = self._search_paths(context.name, context.path)

      AttributeError: 'str' object has no attribute 'name'

      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.

error: metadata-generation-failed

× Encountered error while generating package metadata.

╰─> See above for output.

note: This is an issue with the package mentioned above, not pip.

hint: See above for details.

The command "pip install -e ." failed and exited with 1 during .

Your build has been stopped.
Could you take a look at this issue?
AntonKueltz / fastecdsa

Fix syntax warning in docstring #85
