Fix references in CWG1780 as per discussion on c++std-core.

Author: Dawn Perchik

source/expressions.tex

@@ -1131,8 +1131,8 @@
 
 \pnum
 A member of a closure type shall not be
-explicitly instantiated~(\ref{temp.inst}),
-explicitly specialized~(\ref{temp.explicit}), or
+explicitly instantiated~(\ref{temp.explicit}),
+explicitly specialized~(\ref{temp.expl.spec}), or
 named in a \tcode{friend} declaration~(\ref{class.friend}).
 
 \pnum