Don't use fmt.Fscanf for /proc/sys/kernel/cap_last_cap
Don't use fmt.Fscanf for /proc/sys/kernel/cap_last_cap

fmt.Fscanf reads byte by byte from this file, but
this doesn't work for sysctl-s.

29279 open("/proc/sys/kernel/cap_last_cap", O_RDONLY|O_CLOEXEC
29279 <... open resumed> ) = 3
29279 read(3, "3", 1) = 1
29279 read(3, "", 1) = 0

Reported-by: da39a3ee5e6b4b0d3255bfef95601890afd80709@syndtr

syndtr/gocapability,tianon/debian-golang-gocapability