Added default value to the checkerboard node

MaterialGraphProject/Assets/UnityShaderEditor/Runtime/Nodes/Procedural/CheckerboardNode.cs

 
         protected override MaterialSlot GetInputSlot2()
         {
-            return new MaterialSlot(InputSlot2Id, GetInputSlot2Name(), kInputSlot2ShaderName, UnityEngine.Graphing.SlotType.Input, SlotValueType.Vector1, Vector4.zero);
+            return new MaterialSlot(InputSlot2Id, GetInputSlot2Name(), kInputSlot2ShaderName, UnityEngine.Graphing.SlotType.Input, SlotValueType.Vector1, new Vector4(10,0,0,0));
-            return new MaterialSlot(InputSlot3Id, GetInputSlot3Name(), kInputSlot3ShaderName, UnityEngine.Graphing.SlotType.Input, SlotValueType.Vector1, Vector4.zero);
+            return new MaterialSlot(InputSlot3Id, GetInputSlot3Name(), kInputSlot3ShaderName, UnityEngine.Graphing.SlotType.Input, SlotValueType.Vector1, new Vector4(10, 0, 0, 0));
         }
         protected override MaterialSlot GetOutputSlot()
         {