fix: incorrect development status in setup.py

Author: erikwrede

setup.py

@@ -32,7 +32,7 @@
     license='MIT',
 
     classifiers=[
-        'Development Status :: 3 - Beta',
+        'Development Status :: 4 - Beta',
         'Intended Audience :: Developers',
         'Topic :: Software Development :: Libraries',
         'Programming Language :: Python :: 3.6',