[vector.cons] vector(const Allocator&) should be noexcept (#2182)

This fixes an oversight in the wording of
"N4258: Cleaning‐up noexcept in the Library",
which updated the overview, but not the description.

Author: jensmaurer

source/containers.tex

@@ -5274,7 +5274,7 @@
 
 \indexlibrary{\idxcode{vector}!constructor}
 \begin{itemdecl}
-explicit vector(const Allocator&);
+explicit vector(const Allocator&) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}