Fix format specifier for boolean value.

Change-Id: I33bf9aa0487588e0d296e612bce51d181e49d6d3
Reviewed-on: http://review.couchbase.org/42499
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>