Incorrect pyparsing compatibility notes in README

[ptmcg]

Note that you may encounter an error while installing pyparsing on which json2xlsx
depends. This is probably because pyparsing 1.x runs only on Python 2.x while
pyparsing 2.x runs only on Python 3.x. Currently, json2xlsx declares in the package
that pyparsing 1.x is required, which means that Python 3.x users must install
json2xlsx from GitHub with manual modificatin to setup.py. I do not use Python 3.x
often, so please let me know a workaround.

Pyparsing 2.4.7 is compatible with both Python 2.7 and Python 3.x Pyparsing 3.0.0 is the first pyparsing version that is not compatible with Python 2.7.