feat(docz): render [Empty String] on PropsTable (#427)

* Updates the PropsTable to render '[Empty String]' instead of nothing.
* Add the code to print [No Default]

packages/docz/src/components/PropsTable.tsx

@@ -12,7 +12,7 @@ export interface StylesMap {
 
 const styles: StylesMap = {
   thead: {
-    textAlign: 'left'
+    textAlign: 'left',
   },
 }