F.52: Improve language just a bit (#1770)

CppCoreGuidelines.md

@@ -3895,7 +3895,7 @@ Unfortunately, there is no simple way to capture by reference to `const` to get
 
 ##### Example
 
-Here, a large object (a network message) is passed to an iterative algorithm, and is it not efficient or correct to copy the message (which might not be copyable):
+Here, a large object (a network message) is passed to an iterative algorithm, and it is not efficient or correct to copy the message (which might not be copyable):
 
     std::for_each(begin(sockets), end(sockets), [&message](auto& socket)
     {