[utility] Change 'nonzero' to more appropriate words. (#1575)

Author: cpplearner

source/utilities.tex

@@ -6474,7 +6474,7 @@
 \effects
 Stores a new value in the bit at position \tcode{pos} in
 \tcode{*this}.
-If \tcode{val} is nonzero, the stored value is one, otherwise it is zero.
+If \tcode{val} is \tcode{true}, the stored value is one, otherwise it is zero.
 
 \pnum
 \returns
@@ -10356,7 +10356,7 @@
 \returns
 \begin{itemize}
 \item When \tcode{dynamic_cast<typename shared_ptr<T>::element_type*>(r.get())}
-returns a nonzero value \tcode{p}, \tcode{shared_ptr<T>(r, p)}.
+returns a non-null value \tcode{p}, \tcode{shared_ptr<T>(r, p)}.
 \item Otherwise, \tcode{shared_ptr<T>()}.
 \end{itemize}