Add custom shader_version on glow renderer (#1993)

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

examples/retained_image/src/main.rs

@@ -8,6 +8,7 @@ fn main() {
         initial_window_size: Some(egui::vec2(500.0, 900.0)),
         ..Default::default()
     };
+
     eframe::run_native(
         "Show an image with eframe/egui",
         options,