Make EditSession#center (//center) set even y blocks.

At some point this was fixed for x and z but never for y...

worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java

@@ -1028,8 +1028,10 @@ public class EditSession implements Extent, AutoCloseable {
         Region centerRegion = new CuboidRegion(
                 getWorld(), // Causes clamping of Y range
                 BlockVector3.at(((int) center.getX()), ((int) center.getY()), ((int) center.getZ())),
-                BlockVector3.at(MathUtils.roundHalfUp(center.getX()),
+                BlockVector3.at(
-                            center.getY(), MathUtils.roundHalfUp(center.getZ())));
+                        MathUtils.roundHalfUp(center.getX()),
+                        MathUtils.roundHalfUp(center.getY()),
+                        MathUtils.roundHalfUp(center.getZ())));
         return setBlocks(centerRegion, pattern);
     }