refactor: Drop support for Python 2

Author: pawamoy

src/git_changelog/build.py

@@ -1,5 +1,3 @@
-from __future__ import print_function
-
 import sys
 from datetime import datetime
 from subprocess import check_output  # nosec

src/git_changelog/cli.py

@@ -15,8 +15,6 @@
 Also see http://click.pocoo.org/5/setuptools/#setuptools-integration.
 """
 
-from __future__ import print_function
-
 import argparse
 import sys
 

src/git_changelog/providers.py

@@ -22,7 +22,7 @@ def __str__(self):
         return self.ref + ": " + self.url
 
 
-class ProviderRefParser(object):
+class ProviderRefParser:
     REF = {}
 
     def get_refs(self, ref_type, text):