CH2: Correct Bernoulli failure probability

This was fixed in 3fe9939b38dbfd3547f15080232ae49caf262cec but unrelated
changes in 16c6a7778792088cf15d63836c359133d5cded7f reverted the fix.
Merge pull request #127 from kyleam/bern-prop-failure

CH2: Correct Bernoulli failure probability