[basic.scope.contract] Fix typo

Author: lprv

source/basic.tex

@@ -1618,7 +1618,7 @@
 \item
 if associated with a \grammarterm{lambda-declarator},
 the nearest enclosing lambda scope
-of the precondition assertion\iref{expr.prim.lambda},
+of the postcondition assertion\iref{expr.prim.lambda},
 \end{itemize}
 the program is ill-formed.