CI Action: Use poetry

Author: tony

.github/workflows/libtmux-ci.yml

@@ -43,18 +43,18 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install python dependencies
       run: |
-        python -m pip install --upgrade pip pipenv setuptools
-        pipenv install -d --system --skip-lock
+        python -m pip install --upgrade poetry
+        poetry install
     - name: Lint with flake8
       run: |
-        pipenv run flake8
+        poetry run flake8
     - name: Test with pytest
       continue-on-error: ${{ matrix.tmux-version == 'master' }}
       run: |
         export PATH=$HOME/tmux-builds/tmux-${{ matrix.tmux-version }}/bin:$PATH
         ls $HOME/tmux-builds/tmux-${{ matrix.tmux-version }}/bin
         tmux -V
-        pipenv run py.test --cov=./ --cov-report=xml
+        poetry run py.test --cov=./ --cov-report=xml
     - uses: codecov/codecov-action@v1
       with:
         token: ${{ secrets.CODECOV_TOKEN }}