add a recipe to create cobble

4 pumice + 4 basalt = 8 cobble

so that players can still build stone generators with the help of
machines in e.g. basic_machines or pipeworks

crafts.lua

@@ -298,6 +298,21 @@ minetest.register_craft({
 	}
 })
 
+minetest.register_craft({
+	type = "shapeless",
+	output = "default:cobble 8",
+	recipe = {
+		"gloopblocks:pumice",
+		"gloopblocks:pumice",
+		"gloopblocks:pumice",
+		"gloopblocks:pumice",
+		"gloopblocks:basalt",
+		"gloopblocks:basalt",
+		"gloopblocks:basalt",
+		"gloopblocks:basalt"
+	}
+})
+
 minetest.register_craft({
 	output = "gloopblocks:fence_steel 1",
 	recipe = {