Minor cleanup

src/chip8.rs

@@ -277,7 +277,7 @@ mod tests {
 
     #[test]
     fn it_maps_physical_keys_to_virtual_ones() {
-        let mut chip8 = Chip8::new();
+        let chip8 = Chip8::new();
         assert_eq!(chip8.keyboard_map(Keycode::A), Some(7));
         assert_eq!(chip8.keyboard_map(Keycode::X), Some(0));
         assert_eq!(chip8.keyboard_map(Keycode::M), None);
@@ -294,7 +294,7 @@ mod tests {
 
     #[test]
     fn it_has_a_default_character_set() {
-        let mut chip8 = Chip8::new();
+        let chip8 = Chip8::new();
         assert_eq!(chip8.memory[0..5], [0xf0, 0x90, 0x90, 0x90, 0xf0])
     }
 }

src/main.rs

@@ -1,5 +1,5 @@
 use sdl2::event::Event;
-use sdl2::keyboard::{Keycode, Scancode};
+use sdl2::keyboard::Keycode;
 use sdl2::pixels::Color;
 use sdl2::rect::Rect;