title: Use of unresolved identifier 'SyncCredentials'
body: <p>i am new to realm and ios development. I was following realm tutorial for build a full sync app on their website
  <a href="https://docs.realm.io/sync/getting-started-1/step-1-my-first-realm-app" rel="nofollow noreferrer">https://docs.realm.io/sync/getting-started-1/step-1-my-first-realm-app</a>.</p>
  <p>The app keep showing this error</p>
  <blockquote>
  <p>Use of unresolved identifier 'SyncCredentials'</p>
  </blockquote>
  <p>here is my code</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>import RealmSwift
  
  @objc func signIn() {
      logIn(username: username!, password: password!, register: false)
  }
  
  @objc func signUp() {
      logIn(username: username!, password: password!, register: true)
  }
  
  // Log in with the username and password, optionally registering a user.
  func logIn(username: String, password: String, register: Bool) {
      print("Log in as user: \(username) with register: \(register)");
      setLoading(true);
      let creds = SyncCredentials.usernamePassword(username: username, password: password, register: register);
      SyncUser.logIn(with: creds, server: Constants.AUTH_URL, onCompletion: { [weak self](user, err) in
          self!.setLoading(false);
          if let error = err { 
              // Auth error: user already exists? Try logging in as that user.
              print("Login failed: \(error)");
              self!.errorLabel.text = "Login failed: \(error.localizedDescription)"
              return;
          }
          print("Login succeeded!");
          self!.navigationController!.pushViewController(ItemsViewController(), animated: true);
      });
  }</code></pre>
  </div>
  </div>
  </p>
  <p>how can I fix this error?</p>