Don't swallow revert reason when executing transaction.

[MicahZoltu]

zodiac-modifier-delay/contracts/Delay.sol

Line 200 in 515737f

require(exec(to, value, data, operation), "Module transaction failed");

Calling exec results in the revert reason being lost, which makes debugging failure incredibly difficult. With a revert reason it would take a couple seconds to figure out why the transaction being called failed, but without it takes hours.