Fix grammar-o in comment.

llvm-svn: 225324
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index a57a920..b84ea7b 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -13015,7 +13015,7 @@
     Pos = VTablesUsed.insert(std::make_pair(Class, DefinitionRequired));
   if (!Pos.second) {
     // If we already had an entry, check to see if we are promoting this vtable
-    // to required a definition. If so, we need to reappend to the VTableUses
+    // to require a definition. If so, we need to reappend to the VTableUses
     // list, since we may have already processed the first entry.
     if (DefinitionRequired && !Pos.first->second) {
       Pos.first->second = true;