use btn-secondary as default button style for bootstrap 4

Author: AllenFang

src/pagination/SizePerPageDropDown.js

@@ -53,7 +53,7 @@ SizePerPageDropDown.propTypes = {
 SizePerPageDropDown.defaultProps = {
   open: false,
   hidden: false,
-  btnContextual: 'btn-default',
+  btnContextual: 'btn-default btn-secondary',
   variation: 'dropdown',
   className: ''
 };

src/toolbar/ClearSearchButton.js

@@ -35,7 +35,7 @@ ClearSearchButton.propTypes = {
   onClick: PropTypes.func
 };
 ClearSearchButton.defaultProps = {
-  btnContextual: 'btn-default',
+  btnContextual: 'btn-default btn-secondary',
   className: '',
   btnText: 'Clear',
   onClick: undefined