Fix render to string test case

src/render/string.rs

@@ -106,7 +106,7 @@ fn test_render_to_string() {
         Color::Light, Color::Dark,
     ];
     let image: String = Renderer::<char>::new(colors, 2, 1).build();
-    assert_eq!(&image, "    \n #  \n  # \n    ");
+    assert_eq!(&image, "    \n █  \n  █ \n    ");
 
     let image2 = Renderer::new(colors, 2, 1)
         .light_color("A")