docs: fix code snippets that do not compile

docs/auth/email-link-auth.md

@@ -99,7 +99,6 @@ To initiate the authentication flow, present an interface that prompts the user
             email: emailAuth, actionCodeSettings: acs)
         .catchError((onError) => print('Error sending email verification $onError'))
         .then((value) => print('Successfully sent email verification'));
-    });
     ```
 
 

docs/perf-mon/_custom-code-traces.md

@@ -151,7 +151,7 @@ Note the following:
   not use this type of custom attribute in your app):
 
   ```dart
-  customTrace.putAttribute(("email", user.getEmailAddress());  // Don't do this!
+  customTrace.putAttribute("email", user.getEmailAddress());  // Don't do this!
   ```
 
   Data that exposes any personally identifiable information is subject to

packages/firebase_core/firebase_core_platform_interface/lib/src/method_channel/method_channel_firebase_app.dart

@@ -11,7 +11,7 @@ part of '../../firebase_core_platform_interface.dart';
 /// instance, for example:
 ///
 /// ```dart
-/// Firebase.app('SecondaryApp`);
+/// Firebase.app('SecondaryApp');
 /// ```
 class MethodChannelFirebaseApp extends FirebaseAppPlatform {
   // ignore: public_member_api_docs

packages/firebase_core/firebase_core_web/lib/src/firebase_app_web.dart

@@ -7,11 +7,11 @@ part of '../firebase_core_web.dart';
 
 /// The entry point for accessing a Firebase app instance.
 ///
-/// To get an instance, call the the `app` method on the [FirebaseCore]
+/// To get an instance, call the `app` method on the [FirebaseCore]
 /// instance, for example:
 ///
 /// ```dart
-/// Firebase.app('SecondaryApp`);
+/// Firebase.app('SecondaryApp');
 /// ```
 class FirebaseAppWeb extends FirebaseAppPlatform {
   FirebaseAppWeb._(String name, FirebaseOptions options) : super(name, options);