Corrected PyPI classifier.

Author: panosl

setup.py

@@ -103,7 +103,7 @@ def find_version(*parts):
         'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
-        'Programming Language :: Python :: Implementation :: PyPy3',
+        'Programming Language :: Python :: Implementation :: PyPy',
         'Topic :: Internet :: WWW/HTTP',
         'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
     ],