[rand.adapt.general] apply ref fix from LWG 2181

Author: jwakely

source/numerics.tex

@@ -3187,7 +3187,7 @@
 
 \pnum
 Each type instantiated
-from a class template specified in this section~\ref{rand.eng}
+from a class template specified in this section~\ref{rand.adapt}
 satisfies the requirements
 of a random number engine adaptor~(\ref{rand.req.adapt}) type.