Fix Basic Examples

[nskins]

If one runs the command elixir multi_input_example.exs, the following error occurs (the same error also occurs for the multi_output_example.exs file):

** (FunctionClauseError) no function clause matching in Axon.input/2    
    
    The following arguments were given to Axon.input/2:
    
        # 1
        "x1"
    
        # 2
        [shape: {nil, 1}]
    
    Attempted function clauses (showing 1 out of 1):
    
        def input(input_shape, name) when is_tuple(input_shape) and is_binary(name)
    
    (axon 0.1.0) lib/axon.ex:411: Axon.input/2
    multi_input_example.exs:11: XOR.build_model/2
    multi_input_example.exs:34: XOR.run/0

I determined that this was because the parameters for Axon.input/2 have changed since v0.1.0. I figured that the best resolution would be to update the dependencies in the examples to keep things up-to-date. This was the only change required. As you can see, I left :exla alone in the multi_output_example.exs script since it is commented out. Let me know if anything should change there.

I'd be happy to to take a look at the rest of the examples if you are satisfied with this PR. I think the other examples are still using v0.1.0; however, I have not yet run any of those scripts to determine if errors are occurring.