Remove bugtrack_url as not all tools support it, causing warnings

Author: oschwald

setup.py

@@ -27,7 +27,6 @@
     author='Gregory Oschwald',
     author_email='[email protected]',
     url='http://www.maxmind.com/',
-    bugtrack_url='https://github.com/maxmind/GeoIP2-python/issues',
     packages=['geoip2'],
     package_data={'': ['LICENSE']},
     package_dir={'geoip2': 'geoip2'},