style(clippy): enforce clippy use_self lint

Clippy's `use_self` line ensures that `Self` is used instead of the real
name whenever possible. This makes searching easier and cleans up the
code a bit.

src/spotify_api.rs

@@ -56,7 +56,7 @@ impl Default for WebApi {
 }
 
 impl WebApi {
-    pub fn new() -> WebApi {
+    pub fn new() -> Self {
         Self::default()
     }