fixes

04-typestate/src/main.rs

@@ -33,7 +33,7 @@ impl CredentialManager<Unlocked> {
         todo!()
     }
 
-    pub fn get(&mut self, key: &str) -> Option<&str> {
+    pub fn get(&self, key: &str) -> Option<&str> {
         todo!()
     }