Decreased survival mode bonus time

When tiles combine the time does not increases as much. It is now based
on log scale. When 8’s combine 2 seconds is added, 16’s 3 seconds, 32’s
4 seconds…

The time also stops counting down when the game is lost and is reset to
30 seconds after restarting the game.

Updated version 0.6.8 → 0.6.9 and created a new release apk.