[tests] Don't subclass from object for Python 3

test/functional/test_runner.py

@@ -459,7 +459,7 @@ def check_script_list(src_dir):
             # On travis this warning is an error to prevent merging incomplete commits into master
             sys.exit(1)
 
-class RPCCoverage(object):
+class RPCCoverage():
     """
     Coverage reporting utilities for test_runner.