Updated old forum links

src/ChunkMap.cpp

@@ -3081,7 +3081,7 @@ void cChunkMap::cChunkLayer::UnloadUnusedChunks(void)
 		{
 			// The cChunk destructor calls our GetChunk() while removing its entities
 			// so we still need to be able to return the chunk. Therefore we first delete, then nullptrify
-			// Doing otherwise results in bug http://forum.mc-server.org/showthread.php?tid=355
+			// Doing otherwise results in bug https://forum.cuberite.org/thread-355.html
 			delete m_Chunks[i];
 			m_Chunks[i] = nullptr;
 		}