small fix

doc/RTFM.md

@@ -298,7 +298,7 @@ Race freeness at this level can be argued from:
 error[E0499]: cannot borrow `LOW` as mutable more than once at a time
    --> examples/nested_new.rs:100:29
     |
-100 |     LOW.claim_mut_new(b, t, |_low, b, t| {
+100 |     LOW.claim_mut(b, t, |_low, b, t| {
     |     ---                     ^^^^^^^^^^^^ second mutable borrow occurs here
 ```
   Trying to bluntly copy (clone) a resource handler will also fail.