[vector.bool.pspc] Reinstate redundant "inline", as per paper

The "inline" was removed editorially in
2141dab, but CD review has requested
we retain it.

Author: tkoeppe

source/containers.tex

@@ -6110,7 +6110,7 @@
     class vector<bool, Allocator>;
 
   template<class T>
-    constexpr bool @\exposid{is-vector-bool-reference}@ = @\seebelow@;          // \expos
+    inline constexpr bool @\exposid{is-vector-bool-reference}@ = @\seebelow@;   // \expos
 
   // hash support
   template<class T> struct hash;