Fix bs-placeholder usage for jQuery>=3.0
Fix bs-placeholder usage for jQuery>=3.0

jQuery 3.0 introduced a breaking change in the empty value of multi select boxes.
For details, see https://jquery.com/upgrade-guide/3.0/#breaking-change-select-multiple-with-nothing-selected-returns-an-empty-array

anhtranqs3/bootstrap4-select,jesenko/bootstrap-select,silviomoreto/bootstrap-select,anhtranqs3/bootstrap4-select,jesenko/bootstrap-select,silviomoreto/bootstrap-select