fix typo

add a missing bracket

CppCoreGuidelines.md

@@ -2623,7 +2623,7 @@ A `span` represents a range of elements, but how do we manipulate elements of th
         for (int x : s) cout << x << '\n';  // range traversal (guaranteed correct)
         for (int i = 0; i<s.size(); ++i) cout << x << '\n';  // C-style traversal (potentially checked)
         s[7] = 9;                           // random access (potentially checked)
-        std::sort(&s[0],&s[s.size()/2);     // extract pointers (potentially checked)
+        std::sort(&s[0],&s[s.size()/2]);    // extract pointers (potentially checked)
     }
     
 ##### Note