[unique.ptr.single.general] Fix typo

Author: Andreas-Krug

source/memory.tex

@@ -2116,7 +2116,7 @@
 A program that instantiates the definition of \tcode{unique_ptr<T, D>}
 is ill-formed if \tcode{T*} is an invalid type.
 \begin{note}
-This prevents the intantiation of specializations such as
+This prevents the instantiation of specializations such as
 \tcode{unique_ptr<T\&, D>} and \tcode{unique_ptr<int() const, D>}.
 \end{note}