Custom activation function example error: "Der" does not give a valid preprocessing token

[GiorgosXou]

That's why you should always make sure about comments in front of preprocessor-directives:

NeuralNetworks/examples/Other/Custom_activation_function/Custom_activation_function.ino

Lines 3 to 4 in da5b5af

	#define CUSTOM_AF1 my_sigmoid // My "custom" activation function
	#define CUSTOM_DF1 // Comment to disable Derivative function

Just remove comments to fix it lol