adjust style

src/client/js/components/Admin/App/SesSetting.jsx

@@ -69,7 +69,7 @@ function SmtpSetting(props) {
         </div>
 
         <div className="row my-3">
-          <div className="offset-5">
+          <div className="mx-auto">
             <button type="button" className="btn btn-primary" onClick={submitHandler} disabled={adminAppContainer.state.retrieveError != null}>
               { t('Update') }
             </button>