title: Beeware 'briefcase create' asks for cairo >= 1.15.10
body: <p>I'm following Beeware tutorial and unable to 'briefcase create'.</p>
  <p>At some point it shows this:</p>
  <pre><code>Collecting pygobject&gt;=3.14.0
    Downloading PyGObject-3.38.0.tar.gz (712 kB)
       |████████████████████████████████| 712 kB 6.9 MB/s 
    Installing build dependencies ... error
    ERROR: Command errored out with exit status 1:
     command: /usr/bin/python3.8 /usr/local/lib/python3.8/dist-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-6esqaemw/overlay --no-warn-script-location --no-binary :none: --only-binary :none: -i https://pypi.org/simple -- setuptools wheel pycairo
         cwd: None
    Complete output (36 lines):
    WARNING: The directory '/home/brutus/.cache/pip' or its parent directory is not owned or is not writable by the current user. The cache has been disabled. Check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
    Collecting setuptools
      Downloading setuptools-50.3.2-py3-none-any.whl (785 kB)
    Collecting wheel
      Downloading wheel-0.35.1-py2.py3-none-any.whl (33 kB)
    Collecting pycairo
      Downloading pycairo-1.20.0.tar.gz (344 kB)
      Installing build dependencies: started
      Installing build dependencies: finished with status 'done'
      Getting requirements to build wheel: started
      Getting requirements to build wheel: finished with status 'done'
        Preparing wheel metadata: started
        Preparing wheel metadata: finished with status 'done'
    Building wheels for collected packages: pycairo
      Building wheel for pycairo (PEP 517): started
      Building wheel for pycairo (PEP 517): finished with status 'error'
      ERROR: Command errored out with exit status 1:
       command: /usr/bin/python3.8 /usr/local/lib/python3.8/dist-packages/pip/_vendor/pep517/_in_process.py build_wheel /tmp/tmp426eh9du
           cwd: /tmp/pip-install-rmj9v5en/pycairo
      Complete output (12 lines):
      running bdist_wheel
      running build
      running build_py
      creating build
      creating build/lib.linux-x86_64-3.8
      creating build/lib.linux-x86_64-3.8/cairo
      copying cairo/__init__.py -&gt; build/lib.linux-x86_64-3.8/cairo
      copying cairo/__init__.pyi -&gt; build/lib.linux-x86_64-3.8/cairo
      copying cairo/py.typed -&gt; build/lib.linux-x86_64-3.8/cairo
      running build_ext
      Requested 'cairo &gt;= 1.15.10' but version of cairo is 1.14.6
      Command '['pkg-config', '--print-errors', '--exists', 'cairo &gt;= 1.15.10']' returned non-zero exit status 1.
      ----------------------------------------
      ERROR: Failed building wheel for pycairo
    Failed to build pycairo
    ERROR: Could not build wheels for pycairo which use PEP 517 and cannot be installed directly
    ----------------------------------------
  ERROR: Command errored out with exit status 1: /usr/bin/python3.8 /usr/local/lib/python3.8/dist-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-6esqaemw/overlay --no-warn-script-location --no-binary :none: --only-binary :none: -i https://pypi.org/simple -- setuptools wheel pycairo Check the logs for full command output.
  Unable to install dependencies. This may be because one of your dependencies is invalid, or because pip was unable to connect to the PyPI server. 
  </code></pre>
  <p>I believe the main problem is</p>
  <pre><code> Requested 'cairo &gt;= 1.15.10' but version of cairo is 1.14.6
  </code></pre>
  <p>But what I don't understand is were is cairo 1.14.6 if I have only cairo 1.20.0 installed.</p>
  <p>I tried to update docker, reinstall cairo and pycairo, updated python packages but the error is still there.</p>