drop support for python 2.6

Author: mvexel

setup.py

@@ -13,7 +13,6 @@
     keywords=['openstreetmap', 'overpass', 'wrapper'],
     classifiers=[
         'License :: OSI Approved :: Apache Software License',
-        'Programming Language :: Python :: 2.6',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3.3',
         'Programming Language :: Python :: 3.4',