Support for Juno/iPad - Consider removing dependency on past.builtins and future.utils

Hi, I’ve been using Juno (Jupyter on iPad) and I had to make two small changes to PyHive to get it to work.

Juno only supports native modules and doesn’t support past.builtins. You only seem to use to in escape_item so I replaced the isinstance of basestring with isinstance of str, unicode. That may break Python 2 compatibility. I’ve never used python 2...

Juno also doesn’t support future.utils so I replace it with a link to six (which it does support). Six implements with_metaclass so I just replaced the import to future.utils to an import to six.

I’m a python novice (I’m only as few weeks into the language) so I’m not sure what I’m doing, but I thought that this might be helpful.