displayHex fix

[hastypete]

displayHex(16) should show zero, but shows 1
(since of course '0' comes after 'F')
That way no matter what number you send, you will see the lower nibble correctly.

[hastypete]

Here is fix:
Add a line to displayHex as such:
uint8_t offset = 0;
hex = hex % 16; <<<< This is the added line. Mod makes sure no matter what the value is it will be 0-15
if (hex <= 9)

For model 1. I don't have model 2 to work with to fix that.

[hastypete]

I'm learning how to do pull requests from someone. This is my first try. I hope it is good.