improve how markdown code language is commented

We added a space between the markdown triple code mark
and language that was enclosed in HTML comments.

So a line of the form:

````
```<!---c--->
````

became:

````
``` <!---c--->
````

This was done to **help** some code see that the HTML comment
string was not a markdown code specifier.   Not all code
understands this after this changed.  For example, `pandoc(1)`
still forms HTML classes of the form "&lt;!---c--&gt;"
when it encounters the above mentioned change.

We also fixed a problem with `2019/dogon/README.md` regarding
a markdown code block.

We also fixed a problem with `2020/yang/README.md` regarding
a markdown code block.

2020/ferguson1/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [2020 ferguson1 bugs](../../bugs.html#2020_fer
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     WAIT=N WALLS=[01] EVADE=N SIZE=N MAXSIZE=N GROW=N SHEDS=N SHED=N CANNIBAL=[01] ./prog
     # start pressing some arrow keys
 ```
@@ -87,7 +87,7 @@ and non-zero).
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     make test
 
     WAIT=75 WALLS=1 CANNIBAL=1 ./prog
@@ -211,7 +211,7 @@ features.
 Because all IOCCC entries should have a man page I have included one (even
 though much of it is what's also above). To render try:
 
-```<!---sh-->
+``` <!---sh-->
     man ./snake.1
 ```