Added missed limiters for Visual Shader node enums

doc/classes/VisualShaderNodeVectorDerivativeFunc.xml

@@ -25,5 +25,8 @@
 		<constant name="FUNC_Y" value="2" enum="Function">
 			Derivative in [code]y[/code] using local differencing.
 		</constant>
+		<constant name="FUNC_MAX" value="3" enum="Function">
+			Represents the size of the [enum Function] enum.
+		</constant>
 	</constants>
 </class>