buttonType should be customizable

.storybook/__snapshots__/Storyshots.test.js.snap

@@ -91,7 +91,7 @@ exports[`Storyshots Dropdown basic usage 1`] = `
   <button
     aria-expanded={false}
     aria-haspopup="true"
-    className="btn-borderless dropdown-toggle btn btn-secondary"
+    className="dropdown-toggle btn btn-light"
     onBlur={[Function]}
     onClick={[Function]}
     onKeyDown={[Function]}

src/Dropdown/Dropdown.scss

 @import "~bootstrap/scss/_dropdown";
 
-.btn-borderless {
-    border: 0 !important;
-}
-
 // Trying to patch this upstream, then this can
 // be removed.
 // https://github.com/twbs/bootstrap/pull/23990

src/Dropdown/index.jsx

@@ -126,12 +126,11 @@ class Dropdown extends React.Component {
         <Button
           aria-expanded={this.state.open}
           aria-haspopup="true"
-          buttonType="secondary"
+          buttonType={this.props.buttonType}
           display={this.props.title}
           onClick={this.toggle}
           onKeyDown={this.handleToggleKeyDown}
           className={[
-            styles['btn-borderless'],
             styles['dropdown-toggle'],
           ]}
           type="button"
@@ -154,11 +153,16 @@ class Dropdown extends React.Component {
 }
 
 Dropdown.propTypes = {
-  title: PropTypes.string.isRequired,
+  buttonType: PropTypes.string,
   menuItems: PropTypes.arrayOf(PropTypes.shape({
     label: PropTypes.string,
     href: PropTypes.string,
   })).isRequired,
+  title: PropTypes.string.isRequired,
+};
+
+Dropdown.defaultProps = {
+  buttonType: 'light',
 };
 
 export default Dropdown;