Fix tonic include guards

BUG=
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1247843002 .
diff --git a/tonic/dart_api_scope.h b/tonic/dart_api_scope.h
index f0f2dc0..da3d2b2 100644
--- a/tonic/dart_api_scope.h
+++ b/tonic/dart_api_scope.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef SKY_ENGINE_TONIC_DART_API_SCOPE_H_
-#define SKY_ENGINE_TONIC_DART_API_SCOPE_H_
+#ifndef TONIC_DART_API_SCOPE_H_
+#define TONIC_DART_API_SCOPE_H_
 
 #include "base/macros.h"
 #include "dart/runtime/include/dart_api.h"
@@ -21,4 +21,4 @@
 
 }  // namespace tonic
 
-#endif  // SKY_ENGINE_TONIC_DART_API_SCOPE_H_
+#endif  // TONIC_DART_API_SCOPE_H_