Is your feature request related to a problem? Please describe.
It is possible to provide a python version as an argument to the dev_setup.sh script. I suggest that the provided version should also be used to install the correct pip. This would make it easier to install mycroft on systems such as respeaker core 2.

Describe the solution you'd like
A clear and concise description of what you want to happen.
I would suggest the following change:

# dev_setup.sh
function install_venv() {
    $opt_python -m venv "${VIRTUALENV_ROOT}/" --without-pip
    curl https://bootstrap.pypa.io/get-pip.py | "${VIRTUALENV_ROOT}/bin/python" - 'pip==20.0.2'
    [[ -x ${VIRTUALENV_ROOT}/bin/pip ]]
}

# dev_setup.sh changes:
function install_venv() {
    $opt_python -m venv "${VIRTUALENV_ROOT}/" --without-pip
    # replace "python" with "$opt_python"
    curl https://bootstrap.pypa.io/get-pip.py | "${VIRTUALENV_ROOT}/bin/${opt_python}" - 'pip==20.0.2'.  # <-----
    [[ -x ${VIRTUALENV_ROOT}/bin/pip ]]
}

Describe alternatives you've considered

Additional context

I am going to create a Pull Request with these change, if others consider it reasonable But first want to discuss about it here.