contrib: require Python 3.6 for byteify-strings.py
This script makes use of `token.COMMENT`, which apparently
isn't present until Python 3.6. So make the script and its
test conditional on Python 3.6.
#!/bin/sh
HGENCODING=UTF-8
export HGENCODING
echo ".. -*- coding: utf-8 -*-" > gendoc.txt
echo "" >> gendoc.txt
LANGUAGE=$1 "$PYTHON" "$TESTDIR/../doc/gendoc.py" >> gendoc.txt 2> /dev/null || exit
echo "checking for parse errors"
"$PYTHON" "$TESTDIR/../doc/docchecker" gendoc.txt
"$PYTHON" "$TESTDIR/../doc/runrst" html gendoc.txt /dev/null