fix: remove tertiary variant from show next dates button

Close #21

Author: paodb

src/main/java/com/flowingcode/vaadin/addons/cronexpressionfield/CronExpressionField.java

@@ -208,7 +208,6 @@ private void configureLayout() {
 
     nextDatesBtn.setText(i18n.getShowNextDatesBtn());
     nextDatesBtn.addClickListener(e -> showNextDates());
-    nextDatesBtn.addThemeVariants(ButtonVariant.LUMO_TERTIARY_INLINE);
     nextDatesBtn.setVisible(false);
 
     add(topLayout, mainLayout, new Span(i18n.getDescriptionLabel()), cronDescriptionDiv, nextDatesBtn);