Making the code of the markdown table the same as the rendered example

doc/user/markdown.md

@@ -1305,7 +1305,7 @@ Example:
 
 ```markdown
 | header 1 | header 2 | header 3 |
-| ---      |  ------  |----------|
+| ---      |  ------  |---------:|
 | cell 1   | cell 2   | cell 3   |
 | cell 4 | cell 5 is longer | cell 6 is much longer than the others, but that's ok. It will eventually wrap the text when the cell is too large for the display size. |
 | cell 7   |          | cell <br> 9 |