towards python 2.x support for deep_mimic (still issue with Logger.print2)

examples/pybullet/gym/pybullet_envs/deep_mimic/env/env.py

@@ -1,4 +1,10 @@
-from abc import ABC, abstractmethod
+from abc import  abstractmethod
+import sys, abc
+if sys.version_info >= (3, 4):
+    ABC = abc.ABC
+else:
+    ABC = abc.ABCMeta('ABC', (), {})
+
 import numpy as np
 from enum import Enum
 
@@ -10,4 +16,4 @@ class Env(ABC):
         
     def __init__(self, args, enable_draw):
         self.enable_draw = enable_draw
-        return
+        return