[basic.fundamental] Ensure consistency with [conv.ptr]

Author: jensmaurer

source/basic.tex

@@ -5317,7 +5317,7 @@
 
 \pnum
 The types denoted by \cv~\tcode{std::nullptr_t} are distinct types.
-A value of type \tcode{std::nullptr_t} is a null pointer
+A prvalue of type \tcode{std::nullptr_t} is a null pointer
 constant\iref{conv.ptr}. Such values participate in the pointer and the
 pointer-to-member conversions\iref{conv.ptr,conv.mem}.
 \tcode{\keyword{sizeof}(std::nullptr_t)} shall be equal to \tcode{\keyword{sizeof}(\keyword{void}*)}.