fix error in 'Development Status' classifier

Author: DanielGoldfarb

setup.py

@@ -27,7 +27,7 @@
       license="BSD-style",
       package_dir={'': pkg_location},
       packages=find_packages(where=pkg_location),
-      classifiers=['Development Status :: 2 - Beta',
+      classifiers=['Development Status :: 4 - Beta',
                    'Programming Language :: Python :: 3',
                    'Programming Language :: Python :: 3.6',
                    'Programming Language :: Python :: 3.7',