Prepare 2.4.2 release with an installation failure on Python 2.7 fix

This addresses a failure when trying to install the package for
Python 2.7.

    Collecting pygtrie
    ⋮
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-install-LyKc02/pygtrie/setup.py", line 177, in <module>
        distutils.core.setup(**kwargs)
    ⋮
      File "/usr/lib/python2.7/distutils/dist.py", line 846, in get_command_obj
        cmd_obj = self.command_obj[command] = klass(self)
    TypeError: object() takes no parameters

Developers who still use Python 2.7 are urged to migrate to
Python 3.x.  2.7 is officially dead and at some point I’ll stop
caring about bugs reported on that version of the language.

Fixes: google#33

setup.py

@@ -36,7 +36,7 @@ def run(self):
                 shutil.rmtree(outdir)
 
 
-class CommandMixin(object):
+class CommandMixin:
     @classmethod
     def _read_and_stat(cls, src):
         from distutils.errors import DistutilsFileError
@@ -75,8 +75,10 @@ def copy_file(self, src, dst, preserve_mode=1, preserve_times=1, link=None,
                           data, re.MULTILINE)
 
         if not m:
-            return super(CommandMixin, self).copy_file(
-                    src, dst, preserve_mode=preserve_mode,
+            # Not using super() for better Python 2.x compatibility (distutils
+            # uses old-style classes).
+            return distutils.core.Command.copy_file(
+                    self, src, dst, preserve_mode=preserve_mode,
                     preserve_times=preserve_times, link=link)
 
         if os.path.isdir(dst):

version-history.rst

@@ -1,10 +1,17 @@
 Version History
 ---------------
 
+2.4.2: 2021/01/03
+
+- Remove use of ‘super’ in ``setup.py`` to fix compatibility with
+  Python 2.7.  This changes build code only; no changes to the library
+  itself.
+
 2.4.1: 2020/11/20
 
 - Remove dependency on ``packaging`` module from ``setup.py`` to fix
-  installation on systems without that package.  [Thanks to Eric
+  installation on systems without that package.  This changes build
+  code only; no changes to the library itself.  [Thanks to Eric
   McLachlan for reporting]
 
 2.4.0: 2020/11/19  [pulled back from PyPi]