Bot fix

https://codereview.chromium.org/1311503008
https://uberchromegw.corp.google.com/i/client.skia/builders/Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Coverage/builds/1083/steps/build%20dm/logs/stdio

BUG=skia:

Review URL: https://codereview.chromium.org/1331463004

gm/emptypath.cpp

@@ -169,7 +169,7 @@ public:
     }
 
 protected:
-    SkString onShortName() {
+    SkString onShortName() override {
         return SkString("emptystroke");
     }