[SPIGOT-461] Use a more appropriate collection for conccurent UserCache

nms-patches/UserCache.patch

@@ -0,0 +1,25 @@
+--- a/net/minecraft/server/UserCache.java
++++ b/net/minecraft/server/UserCache.java
+@@ -42,7 +42,7 @@
+     public static final SimpleDateFormat a = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
+     private final Map<String, UserCache.UserCacheEntry> c = Maps.newHashMap();
+     private final Map<UUID, UserCache.UserCacheEntry> d = Maps.newHashMap();
+-    private final LinkedList<GameProfile> e = Lists.newLinkedList();
++    private final java.util.Deque<GameProfile> e = new java.util.concurrent.ConcurrentLinkedDeque<GameProfile>(); // CraftBukkit
+     private final MinecraftServer f;
+     protected final Gson b;
+     private final File g;
+@@ -323,11 +323,11 @@
+             }
+         }
+ 
+-        public JsonElement serialize(Object object, Type type, JsonSerializationContext jsonserializationcontext) {
++        public JsonElement serialize(UserCacheEntry object, Type type, JsonSerializationContext jsonserializationcontext) { // CraftBukkit - decompile error
+             return this.a((UserCache.UserCacheEntry) object, type, jsonserializationcontext);
+         }
+ 
+-        public Object deserialize(JsonElement jsonelement, Type type, JsonDeserializationContext jsondeserializationcontext) throws JsonParseException {
++        public UserCacheEntry deserialize(JsonElement jsonelement, Type type, JsonDeserializationContext jsondeserializationcontext) throws JsonParseException { // CraftBukkit - decompile error
+             return this.a(jsonelement, type, jsondeserializationcontext);
+         }
+