modify train_ray.py for compatibility

Author: yijiezh

tests/data/ray_cartpole/train_ray.py

@@ -10,7 +10,7 @@
 config["num_gpus"] = int(os.environ.get("SM_NUM_GPUS", 0))
 checkpoint_dir = os.environ.get("SM_MODEL_DIR", "/Users/nadzeya/gym")
 config["num_workers"] = 1
-agent = ppo.PPOAgent(config=config, env="CartPole-v0")
+agent = ppo.PPOTrainer(config=config, env="CartPole-v0")
 
 # Can optionally call agent.restore(path) to load a checkpoint.