setup.py: use the correct license classifier

twine refuses to upload with "GPL-2". The support classifiers are found
on <https://pypi.org/classifiers>

Author: mgerstner

setup.py

@@ -50,7 +50,7 @@ def getLongDesc():
 		#url = 'https://github.com/mgerstner/oscfs',
 		classifiers = [
 			'Intended Audience :: Developers',
-			'License :: OSI Approved :: GPL-2',
+			'License :: OSI Approved :: GNU General Public License v2 (GPLv2)',
 			'Programming Language :: Python :: 2.7',
 			'Topic :: System :: Filesystems'
 		],