fix compiler warning in example skia_svg_render.

examples/skia_svg_render.cc

@@ -56,7 +56,7 @@ int main(int argc, char *argv[]) {
     uint8_t *dataPtr = const_cast<uint8_t*>(data->bytes());
 
     std::ofstream out(argv[2], std::ios::binary);
-    for (int i = 0; i < data->size(); ++i) {
+    for (size_t i = 0; i < data->size(); ++i) {
         out.write(reinterpret_cast<char*>(&dataPtr[i]), 1);
     }