fix/update-nom-to-5.1.x: Update the "nom" dependency to 5.1.x so that nom::Err can correctly inherit std::error::Error

[p1-mmr]

This pull request will update the "nom" dependency to 5.1.x so that nom::Err can correctly inherit std::error::Error, following this commit: https://github.com/Geal/nom/commit/7952b6909e2e6d315fe6344d14fad084fe98bf89

This is useful because it allows users, when mixing nom function calls with non-nom function calls, to use a generic Result<T, Box<dyn Error>> return type and to use the ? error handling operator, which makes the code way more readable.

[chifflier]

I thought this would not be a problem (cargo always picks 5.1 because of versioning rules). Anyway, it is more correct to depend on 5.1 Applied, thanks