Semantic accuracy in borrow scope rules.

The text claimed 'any borrow must last for a _smaller_ scope than the
owner', however the accurate way of describing the comparison is
inclusive (i.e., 'less than or equal to' vs. 'less than').

Author: nsimplex

src/doc/trpl/references-and-borrowing.md

@@ -151,9 +151,9 @@ As it turns out, there are rules.
 
 Here’s the rules about borrowing in Rust:
 
-First, any borrow must last for a smaller scope than the owner. Second, you may
-have one or the other of these two kinds of borrows, but not both at the same
-time:
+First, any borrow must last for a scope no greater than that of the owner.
+Second, you may have one or the other of these two kinds of borrows, but not
+both at the same time:
 
 * one or more references (`&T`) to a resource.
 * exactly one mutable reference (`&mut T`)