Use python-version in the example for consistency

[hugovk]

version is deprecated in 6f6fcee and python-version should be used instead, like in the README:

jobs:
  build:
    runs-on: ubuntu-16.04
    strategy:
      matrix:
        python: [ '2.x', '3.x', 'pypy3' ]
    name: Python ${{ matrix.python }} sample
    steps:
      - uses: actions/checkout@master
      - name: Setup python
        uses: actions/setup-python@v1
        with:
          python-version: ${{ matrix.python }}
          architecture: x64
      - run: python my_script.py

I wanted a step to only run for a certain Python version, and at first tried checking for matrix.python-version, but it's really matrix.python with the current README:

    - name: Docs
      if: matrix.python == 2.7
      run: |
        pip install sphinx-rtd-theme
        make doccheck

To make things clearer, use python-version in the example for both, as in this PR, so no need to think about two similar but different names, and we can use this:

    - name: Docs
      if: matrix.python-version == 2.7
      run: |
        pip install sphinx-rtd-theme
        make doccheck

---

Plus fix a couple of "python" -> "Python" typos.

[Schlopper]

good

[madhurig]

@hugovk - Thank you for your contribution!

[hugovk]

You're welcome!