Update progression
- fix a possible bug
Update:
- score for next level follow a linear progression
score += TAPS_PER_LEVEL * (level - 1) + TAPS_PER_LEVEL
- speed of the heart increase relative to the linear progression
y = 2 * x + 1
(where x is the level) - size of the heart reduce relative to the linear progression
y = ref - 0.7 * x
when level < 7 (elsey = ref - 4
)