Update iris/atari/alien/config.json

iris/atari/alien/config.json

@@ -124,6 +124,14 @@
             "inputs": ["z", "should_postprocess"]
           }
         },
+        {
+          "name": "decode_obs_tokens",
+          "method_name": "decode_obs_tokens",
+          "signature": 
+          {
+            "inputs": ["obs_tokens", "num_observations_tokens"]
+          }
+        },
         {
           "name": "encode",
           "method_name": "encode",