[swappable.requirements] Merge example comment into one line (#1829)

Avoids having the comment over the closing brace.

Author: JohelEGP

source/lib-intro.tex

@@ -1681,8 +1681,8 @@
 template <class T>
 void lv_swap(T& t1, T& t2) {
   using std::swap;
-  swap(t1, t2);                                 // OK: uses swappable conditions for
-}                                               // lvalues of type \tcode{T}
+  swap(t1, t2);                                 // OK: uses swappable conditions for lvalues of type \tcode{T}
+}
 
 namespace N {
   struct A { int m; };