Update to Minecraft 1.13-pre7

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/Axis.java

@@ -0,0 +1,21 @@
+package org.bukkit;
+
+/**
+ * Represents a mutually perpendicular axis in 3D Cartesian coordinates. In
+ * Minecraft the x, z axes lie in the horizontal plane, whilst the y axis points
+ * upwards.
+ */
+public enum Axis {
+    /**
+     * The x axis.
+     */
+    X,
+    /**
+     * The y axis.
+     */
+    Y,
+    /**
+     * The z axis.
+     */
+    Z;
+}