Buffer doesn't need to be mutable anymore

examples/hello-world.rs

@@ -103,7 +103,7 @@ async fn run() {
                             width: config.width,
                             height: config.height,
                         },
-                        &mut buffer,
+                        &buffer,
                         Color::rgb(255, 255, 255),
                         &mut cache,
                     )

src/text_render.rs

@@ -60,7 +60,7 @@ impl TextRenderer {
         queue: &Queue,
         atlas: &mut TextAtlas,
         screen_resolution: Resolution,
-        buffer: &mut cosmic_text::Buffer<'a>,
+        buffer: &cosmic_text::Buffer<'a>,
         default_color: Color,
         cache: &mut SwashCache,
     ) -> Result<(), PrepareError> {