Add polyfill for vector.copy()

closes #246
You could say I am doing this against better judgement, but this is
really a simple and easy fix for my problem.

.luacheckrc

@@ -7,7 +7,9 @@ read_globals = {
 	vector = {fields = {
 		-- as of 5.0
 		"new", "direction", "distance", "length", "normalize", "floor", "round",
-		"apply", "equals", "sort", "add", "subtract", "multiply", "divide"
+		"apply", "equals", "sort", "add", "subtract", "multiply", "divide",
+		-- polyfilled
+		"copy"
 	}},
 }
 globals = {"worldedit"}
@@ -15,6 +17,9 @@ globals = {"worldedit"}
 -- Ignore these errors until someone decides to fix them
 ignore = {"212", "213", "411", "412", "421", "422", "431", "432", "631"}
 
+files["worldedit/common.lua"] = {
+	globals = {"vector"},
+}
 files["worldedit/test"] = {
 	read_globals = {"testnode1", "testnode2", "testnode3", "area", "check", "place_pattern"},
 }

worldedit/common.lua

@@ -1,6 +1,15 @@
 --- Common functions [INTERNAL].  All of these functions are internal!
 -- @module worldedit.common
 
+-- Polyfill for vector.copy (added in 5.5.0)
+if not vector.copy then
+	local vnew = vector.new
+	vector.copy = function(v)
+		return vnew(v.x, v.y, v.z)
+	end
+end
+
+
 --- Copies and modifies positions `pos1` and `pos2` so that each component of
 -- `pos1` is less than or equal to the corresponding component of `pos2`.
 -- Returns the new positions.