bump version and update classifiers

setup.py

@@ -1,6 +1,6 @@
 from setuptools import setup, find_packages
 
-version = '2.3.1.dev0'
+version = '3.0.0.dev0'
 
 setup(name='plone.locking',
       version=version,
@@ -11,16 +11,12 @@
           "Development Status :: 5 - Production/Stable",
           "Environment :: Web Environment",
           "Framework :: Plone",
-          "Framework :: Plone :: 5.2",
           "Framework :: Plone :: 6.0",
           "Framework :: Plone :: Core",
-          "Framework :: Zope :: 4",
           "Framework :: Zope :: 5",
           "License :: OSI Approved :: GNU General Public License v2 (GPLv2)",
           "Operating System :: OS Independent",
           "Programming Language :: Python",
-          "Programming Language :: Python :: 2.7",
-          "Programming Language :: Python :: 3.7",
           "Programming Language :: Python :: 3.8",
           "Programming Language :: Python :: 3.9",
           "Programming Language :: Python :: 3.10",
@@ -35,7 +31,7 @@
       namespace_packages=['plone'],
       include_package_data=True,
       zip_safe=False,
-      python_requires=">=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*",
+      python_requires=">=3.8",
       extras_require=dict(
         test=[
             'plone.app.contenttypes',