Rename 2020-02-28-test-markdown.md to 2020-02-28-sample-markdown.md

Author: daattali

_posts/2020-02-28-test-markdown.md _posts/2020-02-28-sample-markdown.md_posts/2020-02-28-test-markdown.md renamed to _posts/2020-02-28-sample-markdown.md

@@ -75,4 +75,4 @@ You can add notification, warning and error boxes like this:
 ### Error
 
 {: .box-error}
-**Error:** This is an error box.
+**Error:** This is an error box.