Update to 1.21

Update Addon to Support this pull request : Slimefun/Slimefun4#4248

We will need to change the pom.xml at the end, when there will be an update for 1.21

Author: Tiakin

pom.xml

@@ -106,9 +106,9 @@
         </dependency>
 
         <dependency>
-            <groupId>com.github.TheBusyBiscuit</groupId>
-            <artifactId>Slimefun4</artifactId>
-            <version>RC-27</version>
+            <groupId>com.github.Slimefun</groupId>
+            <artifactId>Slimefun</artifactId>
+            <version>4.9-UNOFFICIAL</version>
             <scope>provided</scope>
             <exclusions>
                 <exclusion>

src/main/java/io/github/thebusybiscuit/dyedbackpacks/DyedBackpacks.java

@@ -38,7 +38,7 @@ public void onEnable() {
         }
 
         Research research = new Research(new NamespacedKey(this, "dyed_backpacks"), 17200, "Dyed Backpacks", 24);
-        ItemGroup itemGroup = new ItemGroup(new NamespacedKey(this, "dyed_backpacks"), new CustomItemStack(PlayerHead.getItemStack(PlayerSkin.fromHashCode(BackpackColor.RED.getTexture())), "&4Dyed Backpacks"), 2);
+        ItemGroup itemGroup = new ItemGroup(new NamespacedKey(this, "dyed_backpacks"), CustomItemStack.create(PlayerHead.getItemStack(PlayerSkin.fromHashCode(BackpackColor.RED.getTexture())), "&4Dyed Backpacks"), 2);
 
         if (cfg.getBoolean("backpacks.small")) {
             createBackpacks(itemGroup, research, SlimefunItems.BACKPACK_SMALL, 9);