Change demo file compatible to python2 (#40)

* Change demo file to python2 compatible

* Add object to classes for compatibility with python2

Author: whikwon

scripts/algorithms/common/abstract/agent.py

@@ -14,7 +14,7 @@
 import torch
 
 
-class AbstractAgent:
+class AbstractAgent(object):
     """Abstract Agent used for all agents.
 
     Attributes:

scripts/algorithms/common/buffer/replay_buffer.py

@@ -11,7 +11,7 @@
 device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
 
 
-class ReplayBuffer:
+class ReplayBuffer(object):
     """Fixed-size buffer to store experience tuples.
 
     Taken from Udacity deep-reinforcement-learning github repository:
@@ -79,7 +79,7 @@ def __len__(self):
         return len(self.buffer)
 
 
-class NStepTransitionBuffer:
+class NStepTransitionBuffer(object):
     """Fixed-size buffer to store experience tuples.
 
     Attributes:

scripts/algorithms/common/buffer/segment_tree.py

@@ -4,7 +4,7 @@
 import operator
 
 
-class SegmentTree:
+class SegmentTree(object):
     """ Create SegmentTree.
 
     Taken from OpenAI baselines github repository:

scripts/algorithms/common/noise.py

@@ -7,7 +7,7 @@
 import numpy as np
 
 
-class GaussianNoise:
+class GaussianNoise(object):
     """Gaussian Noise.
 
     Taken from https://github.com/vitchyr/rlkit
@@ -28,7 +28,7 @@ def sample(self, t=0):
         return np.random.normal(0, sigma, size=self.action_dim)
 
 
-class OUNoise:
+class OUNoise(object):
     """Ornstein-Uhlenbeck process.
 
     Taken from Udacity deep-reinforcement-learning github repository: