[res.on.exception.handling] Use \throws macro

Author: tkoeppe

source/lib-intro.tex

@@ -2927,7 +2927,7 @@
 \Cpp standard library
 \indextext{specifications!C++}%
 that do not have a
-\synopsis{Throws:}
+\throws
 paragraph
 but do have a potentially-throwing
 exception specification