Fix setup import error
Fix setup import error

`import gspread` statement caused requests packaged to be imported before
dependency could be installed. Sole purpose of import was to extract the
__version__ string field on the module.

Solution is to use a regex to read the version string from __init__.py

Fixes #317

paulfitz/gspread,tjyang/gspread,ShivaShinde/gspread,wbrp/gspread,m4rc1e/gspread,nateyoder/gspread,burnash/gspread