Add missing ModuleBase<T> in DI example

docs/guides/commands/samples/dependency_module.cs

@@ -2,7 +2,7 @@ using Discord;
 using Discord.Commands;
 using Discord.WebSocket;
 
-public class ModuleA : ModuleBase
+public class ModuleA : ModuleBase<SocketCommandContext>
 {
     private readonly DatabaseService _database;
 
@@ -19,7 +19,7 @@ public class ModuleA : ModuleBase
     }
 }
 
-public class ModuleB
+public class ModuleB : ModuleBase<SocketCommandContext>
 {
 
     // Public settable properties will be injected