Fixed setup.py classifier.

Author: jeromekelleher

python/setup.py

@@ -65,7 +65,7 @@ def finalize_options(self):
     # TODO setup a tskit developers email address.
     author_email='[email protected]',
     classifiers=[
-        'Development Status :: 2 - Beta',
+        'Development Status :: 4 - Beta',
         'Intended Audience :: Developers',
         'Topic :: Scientific/Engineering :: Bio-Informatics',
         'License :: OSI Approved :: MIT License',