Wrong macro usage in CNN example

[LarsWulfert]

After merging #18 the wrong macro is used when initializing the sigmoid layer in the example "0_Universal/6_CNN/1_CNN_Training_F32/". However, this does not affect the result of the training!

In line 141, instead of

ailayer_sigmoid_f32_t sigmoid_layer_3 = AILAYER_RELU_F32_A();

should be

ailayer_sigmoid_f32_t sigmoid_layer_3 = AILAYER_SIGMOID_F32_A();

should be used.

https://github.com/Fraunhofer-IMS/AIfES_for_Arduino/blob/07a438213f67e8f9d0271417a9f16be97f1597d2/examples/0_Universal/6_CNN/1_CNN_Training_F32/1_CNN_Training_F32.ino#L141C2-L141C65