Update toytext.CliffWalking env version in envs registry (#1334)

Author: abouelsaadat

Diff for: gymnasium/envs/__init__.py

@@ -147,10 +147,16 @@
 )
 
 register(
-    id="CliffWalking-v0",
+    id="CliffWalking-v1",
     entry_point="gymnasium.envs.toy_text.cliffwalking:CliffWalkingEnv",
 )
 
+register(
+    id="CliffWalkingSlippery-v1",
+    entry_point="gymnasium.envs.toy_text.cliffwalking:CliffWalkingEnv",
+    kwargs={"is_slippery": True},
+)
+
 register(
     id="Taxi-v3",
     entry_point="gymnasium.envs.toy_text.taxi:TaxiEnv",