Pipenv support for annotations

[R-Faraji]

Starting from python version 3.7 annotations are supported, any version below that is not which means that some dependencies cannot be resolve, resulting in a failed locking.

Locking Failed! 

Traceback (most recent call last):
  File "/home/"user"/.local/pipx/venvs/pipenv/lib/python3.8/site-packages/pipenv/resolver.py", line 854, in <module>
    main()
  File "/home/"user"/.local/pipx/venvs/pipenv/lib/python3.8/site-packages/pipenv/resolver.py", line 831, in main
    from pipenv.vendor.vistir.misc import replace_with_text_stream
  File "/home/"user"/.local/pipx/venvs/pipenv/lib/python3.8/site-packages/pipenv/__init__.py", line 56, in <module>
    from .cli import cli
  File "/home/"user"/.local/pipx/venvs/pipenv/lib/python3.8/site-packages/pipenv/cli/__init__.py", line 1, in <module>
    from .command import cli  # noqa
  File "/home/"user"/.local/pipx/venvs/pipenv/lib/python3.8/site-packages/pipenv/cli/command.py", line 7, in <module>
    from pipenv.cli.options import (
  File "/home/"user"/.local/pipx/venvs/pipenv/lib/python3.8/site-packages/pipenv/cli/options.py", line 3, in <module>
    from pipenv.project import Project
  File "/home/"user"/.local/pipx/venvs/pipenv/lib/python3.8/site-packages/pipenv/project.py", line 2
    from __future__ import annotations
    ^
SyntaxError: future feature annotations is not defined