exercism/exercism.io — pull request #1032 by pminten (2013-11-21 08:33:33+00:00)
Title: Don't use :math.pow in elixir grains, fix parens

`:math.pow(2, 64) == (:math.pow(2, 64) - 1)` due to rounding issues,
this is not desirable.

Also move some parentheses to fix an error in the example.