replace derive_deref with derive_more

- the latter already used in our transitive dependencies
- derive_more appears better maintained

src/machine/unify.rs

@@ -9,7 +9,7 @@ use crate::types::*;
 use std::cmp::Ordering;
 use std::ops::{Deref, DerefMut};
 
-use derive_deref::*;
+use derive_more::*;
 use fxhash::FxBuildHasher;
 use indexmap::IndexSet;
 use num_order::NumOrd;
@@ -734,6 +734,7 @@ fn bind_with_occurs_check<U: Unifier>(unifier: &mut U, r: Ref, value: HeapCellVa
 }
 
 #[derive(Deref, DerefMut)]
+#[deref(forward)]
 pub(crate) struct DefaultUnifier<'a> {
     machine_st: &'a mut MachineState,
 }