Upgrade BlackArch to 2018.12.01

src/blackarch.ipxe

@@ -9,7 +9,7 @@ goto ${menu}
 set os BlackArch Linux
 menu ${os} Installers
 item --gap Official Releases
-item 2018.06.01 ${space} ${os} 2018.06.01
+item 2018.12.01 ${space} ${os} 2018.12.01
 choose blackarch_version || goto blackarch_exit
 goto blackarch_boot