refactor(datepicker): remove 'unstable' warning (#4941)
refactor(datepicker): remove 'unstable' warning (#4941)


Close #4909
see https://github.com/valor-software/ngx-bootstrap/issues/4909#issuecomment-446547835
valor-software/ngx-bootstrap,valor-software/ng2-bootstrap,valor-software/ngx-bootstrap,valor-software/ng2-bootstrap,valor-software/ngx-bootstrap,valor-software/ngx-bootstrap