[mem.poly.allocator.mem] Fix typo

Author: Andreas-Krug

source/memory.tex

@@ -7792,7 +7792,7 @@
 
 \pnum
 \effects
-Construct a \tcode{T} object in the storage
+Constructs a \tcode{T} object in the storage
 whose address is represented by \tcode{p}
 by uses-allocator construction with allocator \tcode{*this}
 and constructor arguments \tcode{std::forward<Args>(args)...}.