Bump Manjaro to 17.1.8

src/manjaro.ipxe

@@ -9,7 +9,7 @@ goto ${menu}
 set os Manjaro Linux
 menu ${os} Installers
 item --gap Official Releases
-item 17.1.5 ${space} ${os} 17.1.7
+item 17.1.8 ${space} ${os} 17.1.8
 choose manjaro_version || goto manjaro_exit
 
 :manjaro_flavor