Update ExpGPIO class to fix configure initialstate bug

[DoronShapiro]

Currently, if configure is called on a digital out pin from the ExpGPIO class with an initial state, (e.g. ExpGPIO(ioexp, 10).configure(DIGITAL_OUT, 1);, the initial state is treated as a callback and the pin is initialized with its default value of 0.

This commit drops in the updated ExpGPIO class from https://github.com/electricimp/reference/blob/master/hardware/expGpio/expGpio.device.nut that gives ExpGPIO's configure function the same interface as the standard pin's configure function.

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