Don't depend on pipeworks.clone_node - no longer exists

hopper.lua

@@ -7,7 +7,17 @@ minetest.register_craft({
         {"", "default:steel_ingot", ""},
     }
 })
-local hopper = pipeworks.clone_node("default:chest")
+
+local function clone_node(name)
+    local node2 = {}
+    local node = minetest.registered_nodes[name]
+    for k, v in pairs(node) do
+        node2[k] = v
+    end
+    return node2
+end
+
+local hopper = clone_node("default:chest")
 hopper.description = "Hopper"
 hopper.tiles[1] = "pipeworks_filter_side.png"
 hopper.tiles[2] = "pipeworks_filter_side.png"