Correctly mark a method as override.

Signed-off-by: Edward Z. Yang <ezyang@fb.com>
diff --git a/torch/csrc/jit/tracer.cpp b/torch/csrc/jit/tracer.cpp
index ddfedbf..310061a 100644
--- a/torch/csrc/jit/tracer.cpp
+++ b/torch/csrc/jit/tracer.cpp
@@ -33,7 +33,7 @@
     }
   }
 
-  virtual variable_list apply(const variable_list& inputs) {
+  virtual variable_list apply(const variable_list& inputs) override {
     auto should_trace = !flag.test_and_set();
     if (should_trace) enterTrace(inputs);
     auto outputs = Eval::apply(inputs);