docs: Fix the chown command in macvtap-bridge.md

When invoking the script chown shows a warning.

    chown: warning: '.' should be ':': ‘1000.1000’

From `info coreutils 'chown invocation'`.

   Some older scripts may still use ‘.’ in place of the ‘:’ separator.
POSIX 1003.1-2001 (*note Standards conformance::) does not require
support for that, but for backward compatibility GNU ‘chown’ supports
‘.’ so long as no ambiguity results, although it issues a warning and
support may be removed in future versions.  New scripts should avoid the
use of ‘.’ because it is not portable, and because it has undesirable
results if the entire OWNER‘.’GROUP happens to identify a user whose
name contains ‘.’.

Signed-off-by: Wei Liu <liuwe@microsoft.com>

docs/macvtap-bridge.md

@@ -18,7 +18,7 @@ tapindex=$(< /sys/class/net/macvtap0/ifindex)
 tapdevice="/dev/tap$tapindex"
 
 # Ensure that we can access this device
-sudo chown "$UID.$UID" "$tapdevice"
+sudo chown "$UID:$UID" "$tapdevice"
 
 # Use --net fd=3 to point to fd 3 which the shell has opened to point to the /dev/tapN device
 target/debug/cloud-hypervisor \