feat: add Button default variant (primary)

Author: gregberge

src/Button.js

@@ -82,10 +82,11 @@ Button.propTypes = {
   children: PropTypes.node,
   disabled: PropTypes.bool,
   size: PropTypes.oneOf(['sm', 'lg']),
-  variant: PropTypes.oneOf(variants).isRequired,
+  variant: PropTypes.oneOf(variants),
 }
 
 Button.defaultProps = {
+  variant: 'primary',
   theme: defaultTheme,
 }
 

src/Button.md

@@ -4,6 +4,7 @@ Set variants using `variant` prop.
 
 ```js
 <div className="block-list">
+  <Button>Default (primary)</Button>
   <Button variant="primary">Primary</Button>
   <Button variant="secondary">Secondary</Button>
   <Button variant="success">Success</Button>
@@ -12,6 +13,7 @@ Set variants using `variant` prop.
   <Button variant="info">Info</Button>
   <Button variant="light">Light</Button>
   <Button variant="dark">Dark</Button>
+  <Button variant={null}>No variant</Button>
 </div>
 ```