Fix 'one liners tutorial': use 'openat' instead of 'open' in examples
Fix 'one liners tutorial': use 'openat' instead of 'open' in examples

In modern Linux systems (glibc >= 2.26) the open() wrapper was changed
to use the kernel's openat() syscall instead of using the kernel's
open() syscall.

iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace