poetry: poetry-core 1.0.1 release breaks installation poetry via pip

• I am on the latest Poetry version.
• I have searched the issues of this repo and believe that this is not a duplicate.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: ubuntu-latest at GHA
• Poetry version: 1.1.4

Issue

Unfortunately, poetry-core==1.0.1 release breaks poetry, when installed via pip.

Steps to reproduce

1. Create virtual environment for test: python3 -m venv /path/to/venv
2. Install poetry within venv: /path/to/venv/bin/python3 -m pip install poetry==1.1.4
3. Attempt to get help: /path/to/venv/bin/poetry --help
4. Results in error below,

Traceback (most recent call last):
  File "bin/poetry", line 5, in <module>
    from poetry.console import main
  File "/path/to/venv/lib/python3.8/site-packages/poetry/console/__init__.py", line 1, in <module>
    from .application import Application
  File "/path/to/venv/lib/python3.8/site-packages/poetry/console/application.py", line 7, in <module>
    from .commands.about import AboutCommand
  File "/path/to/venv/lib/python3.8/site-packages/poetry/console/commands/__init__.py", line 4, in <module>
    from .check import CheckCommand
  File "/path/to/venv/lib/python3.8/site-packages/poetry/console/commands/check.py", line 2, in <module>
    from poetry.factory import Factory
  File "/path/to/venv/lib/python3.8/site-packages/poetry/factory.py", line 16, in <module>
    from .packages.locker import Locker
  File "/path/to/venv/lib/python3.8/site-packages/poetry/packages/__init__.py", line 2, in <module>
    from .locker import Locker
  File "/path/to/venv/lib/python3.8/site-packages/poetry/packages/locker.py", line 28, in <module>
    from poetry.core.packages.package import Dependency
ImportError: cannot import name 'Dependency' from 'poetry.core.packages.package' (/path/to/venv/python3.8/site-packages/poetry/core/packages/package.py)

How to fix

Install poetry-core==1.0.0 version, when installing poetry via pip.

Reason

poetry.core.packages.package is not a source of Dependency class, it only imports it for type checking: https://github.com/python-poetry/poetry-core/blob/master/poetry/core/packages/package.py#L27

ps. Yes, I understand, that installing poetry via pip is not an official installation method. But at a moment it is an easiest way to install poetry at GitHub Actions