Fix license field

Deniz Dogan · mattrobenolt · commit f2f273d0ebd9 · 2019-02-04T09:10:14.000-08:00
This is useful while filtering packages on PyPI.
diff --git a/setup.py b/setup.py
@@ -180,7 +180,7 @@ class sdist(_sdist):
     author_email='no-reply@pbs.org',
     packages=['ua_parser'],
     package_dir={'': '.'},
-    license='LICENSE.txt',
+    license='Apache 2.0',
     zip_safe=False,
     url='https://github.com/ua-parser/uap-python',
     include_package_data=True,
