make "mUpdateInterval" uint32_t

[wunditta]

On some boards (e.g. ATmega like Uno) "int" is only 2 bytes and thus is capped unsigned at only roughly 65000. As mUpdateInterval holds milliseconds this more or less means that you can have 1 minute max as update interval. I suggest to set the type of mUpdateInterval to uint32_t, which is always right.