The readthedocs build is failing because we do not support Python 3.5 anymore.
Bump the Python version in the configuration.

Fixes: 1b11f28d ("configure: Bump the minimum required Python version to 3.6", 2020-10-02)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20201005150122.446472-1-pbonzini@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

QEMU is all about the Python 3 now so lets also hint that to
ReadTheDocs in its config file.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200206163120.31899-1-alex.bennee@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>