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.

1987/biggar/README.md

@@ -14,7 +14,7 @@ some_command | ./biggar | od -c
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

1987/heckbert/README.md

@@ -17,7 +17,7 @@ To compile on a 16 bit machine, change 300000 to 30000.
 where col is the number of columns to fold at and file is the file to fold.
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

1987/hines/README.md

@@ -12,7 +12,7 @@ make all
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

1987/lievaart/README.md

@@ -13,7 +13,7 @@ make all
 ```
 
 
-### Try:
+## Try:
 
 To see what it would have looked like without the size restrictions:
 

1987/wall/README.md

@@ -16,7 +16,7 @@ make all
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh