Don't require argparse on Python 2.7

[twm]

The dependency on argparse requires it on all Python 2 versions:

uwsgitop/setup.py

Lines 15 to 17 in 423ab88

	install_requires=[
	'argparse;python_version<"3"',
	],

However argparse is part of the standard library in Python 2.7. The dependency should be

    install_requires=[
        'argparse;python_version<"2.7"',
    ],

This would prevent pip install from complaining like this:

...
  Found existing installation: argparse 1.2.1
    Not uninstalling argparse at /usr/lib/python2.7, as it is in the standard library.
    Can't uninstall 'argparse'. No files were found to uninstall.
...