fix docs typos in DurableObject (#431)

* fix docs typos in worker::durable::DurableObject

Fix a syntax error (missing comma) and remove a blank line.

* docs: Remove redundant field name in assignment

If clippy were able to see the code in examples, this would trigger
`clippy::redundant_field_names`.

worker/src/durable.rs

@@ -713,10 +713,9 @@ use worker::*;
 #[durable_object]
 pub struct Chatroom {
     users: Vec<User>,
-    messages: Vec<Message>
+    messages: Vec<Message>,
     state: State,
     env: Env, // access `Env` across requests, use inside `fetch`
-
 }
 
 #[durable_object]
@@ -725,7 +724,7 @@ impl DurableObject for Chatroom {
         Self {
             users: vec![],
             messages: vec![],
-            state: state,
+            state,
             env,
         }
     }