Replace OVERRIDE->override and FINAL->final since we now require C++11.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index f5f1b4041b9e2a26ae16479d366c7f7fb75ec630..c3b0bfcb430868547aa9593ab63036fed5c0d95c 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -1584,9 +1584,9 @@ class ShellArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
 
 class MockArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
  public:
-  void* Allocate(size_t) OVERRIDE { return malloc(1); }
-  void* AllocateUninitialized(size_t length) OVERRIDE { return malloc(1); }
-  void Free(void* p, size_t) OVERRIDE { free(p); }
+  void* Allocate(size_t) override { return malloc(1); }
+  void* AllocateUninitialized(size_t length) override { return malloc(1); }
+  void Free(void* p, size_t) override { free(p); }
 };