Convert hello.py to Python 3

[eseyman]

Support for Python 2 will end on 2020-01-01. Given this, it make sense to move t/Plack-Middleware/cgi-bin/hello.py to use Python 3 instead.

[miyagawa]

how about adding from __future__ import print_function so that it will work with both python 2&3?

i'm ok with converting it to bash or something as well since that's not the point of this test.

[eseyman]

how about adding from __future__ import print_function so that it will work with both python 2&3?

Done.

[miyagawa]

Thanks!