Consider warning about % modulo/format mix-up

[forthrin]

Did Digest::SHA1.hexdigest(it) % 7 to divide items on weekdays, forgetting hexdigest obviously returns a string, not an integer.

The curious thing is that % then goes from modulo to format, since they reuse the same syntax.

Before we get into the should, can Rubocop detect a mix-up like this without false positives?