Fixup: update magic

In reply to:
+/* PMAC0\0\0\0 */
+static const uint64_t pmem_append_cache_magic= 0x0000003043414d50;
In allmost all mariadb code, we usually have a magic prefix of:
255,255,id,version
The current max id is 12, so you could use 13.
sorry, should be 254,254
For example:
uchar    maria_file_magic[]=
{ (uchar) 254, (uchar) 254, (uchar) 9, '\003', };
uchar    maria_pack_file_magic[]=
{ (uchar) 254, (uchar) 254, (uchar) 10, '\001', };
most system have updated 'file' to support mariadb files...

extra/libpmemac/append_cache.c

@@ -31,7 +31,7 @@
 
 
 /* PMAC0\0\0\0 */
-static const uint64_t pmem_append_cache_magic= 0x0000003043414d50;
+static const uint64_t pmem_append_cache_magic= 0x00000000010dfefe;
 
 
 /**