Merge pull request #262 from fabaff/sl

Upgrade Scientific Linux to 7.5/6.10

src/scientific.ipxe

@@ -9,10 +9,10 @@ goto ${menu} ||
 clear osversion
 set os Scientific Linux
 menu ${os} ${arch}
+item 7.5 ${os} 7.5
 item 7.4 ${os} 7.4
-item 7.3 ${os} 7.3
+item 6.10 ${os} 6.10
 item 6.9 ${os} 6.9
-item 6.8 ${os} 6.8
 item other Choose other version [o]
 isset ${osversion} || choose osversion || goto linux_menu
 iseq ${osversion} other || goto scientific_skip_read_osversion