Adjust service collection sample

...according to f89aecb7bf (r141530227)

docs/guides/commands/samples/dependency_map_setup.cs

@@ -1,18 +1,18 @@
-using Discord;
-using Discord.Commands;
-using Discord.WebSocket;
-using foxboat.Services;
+private IServiceProvider _services;
+private CommandService _commands;
 
-public class Commands
+public async Task InstallAsync(DiscordSocketClient client)
 {
-    public async Task Install(DiscordSocketClient client)
-    {
-        // Here, we will inject the ServiceProvider with 
-        // all of the services our client will use.
-        _serviceCollection.AddSingleton(client);
-        _serviceCollection.AddSingleton(new NotificationService());
-        _serviceCollection.AddSingleton(new DatabaseService());
-        // ...
-        await _commands.AddModulesAsync(Assembly.GetEntryAssembly());
-    }
+	// Here, we will inject the ServiceProvider with 
+	// all of the services our client will use.
+	_services = new ServiceCollection()
+					.AddSingleton(client)
+					.AddSingleton(_commands)
+					// You can pass in an instance of the desired type
+					.AddSingleton(new NotificationService())
+					// ...or by using the generic method.
+					.AddSingleton<DatabaseService>()
+					.BuildServiceProvider();
+	// ...
+	await _commands.AddModulesAsync(Assembly.GetEntryAssembly());
 }