[refwrap] Fix wrong use of "shall"

Author: K-ballo

source/utilities.tex

@@ -13262,7 +13262,7 @@
 around a reference to an object or function of type \tcode{T}.
 
 \pnum
-\tcode{reference_wrapper<T>} shall be a trivially copyable type\iref{basic.types}.
+\tcode{reference_wrapper<T>} is a trivially copyable type\iref{basic.types}.
 
 \rSec3[refwrap.const]{\tcode{reference_wrapper} construct/copy/destroy}