tsk-71: Simplify bearer_token() method

src/token.rs

@@ -40,10 +40,9 @@ impl Default for Token {
 }
 
 impl AccessToken {
+    /// Get the token fit for Bearer authentication
     pub fn bearer_token(&self) -> String {
-        let mut token: String = String::from("Bearer ");
-        token += &self.token.clone();
-        token
+        format!("Bearer {}", self.token)
     }
 }