Add clippy, fix up warnings

enkou-shaders/examples/gasket.rs

@@ -78,10 +78,9 @@ pub fn main() -> Result<()> {
     image.save(temp.path()).context("Unable to save image")?;
 
     let open_program: &str = cfg_select! {
-        unix => Some("xdg-open"),
-        _ => None,
-    }
-    .expect("No available program to open images");
+        unix => "xdg-open",
+        _ => panic!("No available program to open images")
+    };
 
     Command::new(open_program)
         .arg(temp.path())