Fix heading level of 'Try' section

It was agreed to be '## Try:' but there were many files where it was
'### Try:'. This has been corrected.

1991/ant/README.md

@@ -18,7 +18,7 @@ NOTE: the file must already exist and not specifying any arg will make the
 program exit without doing anything.
 
 
-### Try:
+## Try:
 
 ```sh
 make hill

1991/brnstnd/README.md

@@ -5,7 +5,7 @@ make all
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

1991/davidguy/README.md

@@ -14,7 +14,7 @@ make all
 where `ip_address` in an IP address of an X server.
 
 
-### Try:
+## Try:
 
 ```sh
 ./davidguy 127.0.0.1:0.0

1991/dds/README.md

@@ -13,7 +13,7 @@ make all
 ```
 
 
-### Try:
+## Try:
 
 The author suggests trying:
 

1991/fine/README.md

@@ -12,7 +12,7 @@ echo text | ./fine
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

1991/westley/README.md

@@ -49,7 +49,7 @@ make nextmove
 ```
 
 
-### Try:
+## Try:
 
 We have provided the shell script, [ttt](ttt.sh), to make it easier to play the
 game: