Update nom to fix Rust compatibility warning?

[wh1t3-r0s3]

Firstly, thank you for your work on procmaps. I've been using it in my project and it's been very helpful.

When I build my project I get the warning: warning: the following packages contain code that will be rejected by a future version of Rust: nom v4.2.3

I see nom is up to v7.1.3, so I think would likely fix it.