expand tabs in recent markdown changes that violate tab_check

2020/ferguson2/README.md

@@ -123,7 +123,7 @@ There is a good deal of useful documentation that is provided with this entry:
     - NOTE: see [recode.html][] (or [recode.html](recode.html) for details about how to decrypt this!
 
 * [testing-procedure][]
-	- How the author tested the code and why it was necessary to do it in the way it was
+        - How the author tested the code and why it was necessary to do it in the way it was
 
 [recode.html]: recode.html
 [enigma.html]: enigma.html