Yep, confirmed.
15 rolls on the current version all resulted in heads.

To fix it change this line in Roll.php

$result['result'] = ((rand(1, 2)) ? 'heads' : 'tails');

to

$result['result'] = ((rand(0, 1)) ? 'heads' : 'tails');

The random number generator seems a bit skewed though.
A test of 15 runs with the 'fix' produced 11 heads to 4 tails.