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.

1990/baruch/README.md

@@ -28,7 +28,7 @@ echo 7 | ./baruch
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 echo 2 | ./baruch

1990/cmills/README.md

@@ -12,7 +12,7 @@ make all
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./cmills 5000

1990/dds/README.md

@@ -12,7 +12,7 @@ make all
 ```
 
 
-### Try:
+## Try:
 
 Give the following lines as input:
 

1990/dg/README.md

@@ -12,7 +12,7 @@ echo foo bar | ./dg
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

1990/jaw/README.md

@@ -5,7 +5,7 @@ make all
 ```
 
 
-### Try:
+## Try:
 
 To test the official C entry, one might try:
 

1990/tbr/README.md

@@ -52,7 +52,7 @@ or ctrl-c (or kill it from another terminal :-) ). But why does it not work with
 just `exit` or `logout`? Hint: see the authors' remarks.
 
 
-### Try:
+## Try:
 
 ```sh
 ./tbr

1990/theorem/README.md

@@ -33,7 +33,7 @@ y1 - initial value  (y(x1) == y1)
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

1990/westley/README.md

@@ -14,7 +14,7 @@ make all
 The number should be greater than 0.
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh