Update 642-language-do.markdown

Author: Joe7M

_build/reference/642-language-do.markdown

@@ -4,18 +4,18 @@
 
 This keyword is used to declare single-line commands. It can be used with WHILE and FOR-family commands.
 
-## Example 1
+### Example 1
 
 ```
 For i = 1 to 10 do print i 
 ```
 
-## Example 2
+### Example 2
 ```
 FOR f IN files("*.txt") DO PRINT f
 ```
 
-## Example 3
+### Example 3
 
 ```
 While(i < 10) do i++