Fix ocs searching app support older version

The ocs search syntax uses x as separater. 1x2x3 means search
1 or 2 or 3. It makes no sense to implode the version array with x.
isAppVersionCompatible() in lib/private/app.php logic means it supports
all major version less than current version. This fix makes the search
logic to be the same as the isAppVersionCompatible.