Canonical signature bad ->cmp check

In 4ef7ddc5e867ad8ca6562851088c374884e5d427 @afk11 replaced `if ($length > 146)` with `if ($math->cmp($length, 146) < 0)` which is incorrect usage of the `cmp` function, it should have been `if ($math->cmp($length, 146) > 0)`
Most likely a copy paste mistake from a few lines above it and tbh I can't blame you because whenever I need to use `bccomp` my head explodes too ...

it fixes #28 ...