Fixing error.

docs/Useful-snippets/snippets.rst

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+Useful Snippets
+===============
+
+A collection of useful code snippets. Here you can find code that allows you to get to get started on common tasks in Mesa.
+
+Models with Discrete Time
+-------------------------
+If you have `Multiple` type agents and one of them has time attribute you can still build a model that is run by discrete time. In this example, each step of the model, and the agents have a time attribute that is equal to the discrete time to run its own step.
+
+.. code:: python
+
+if self.model.schedule.time in self.discrete_time:
+  self.model.space.move_agent(self, new_pos)