fixed mentions in docstring

Signed-off-by: dafnapension <dafnashein@yahoo.com>

src/unitxt/operators.py

@@ -1286,11 +1286,11 @@ class ExecuteExpression(StreamInstanceOperator, ComputeExpressionMixin):
 
     Examples:
        When instance {"a": 2, "b": 3} is process-ed by operator
-       AssignExpression(expression="a+b", to_field = "c")
+       ExecuteExpression(expression="a+b", to_field = "c")
        the result is {"a": 2, "b": 3, "c": 5}
 
        When instance {"a": "hello", "b": "world"} is process-ed by operator
-       AssignExpression(expression = "a+' '+b", to_field = "c")
+       ExecuteExpression(expression = "a+' '+b", to_field = "c")
        the result is {"a": "hello", "b": "world", "c": "hello world"}
 
     """