Change install script to python 3.6

if [ -z "$python_version" ]

then

    echo "Using python 3.5 by default"

    export python_version=3.5

    echo "Using python 3.6 by default"

    export python_version=3.6

else

    echo "Using python "$python_version". But recommended to use python 3.5."

    echo "Using python "$python_version". But recommended to use python 3.6."

fi

if [ -z "$1" ];