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.

2018/algmyr/README.md

@@ -29,7 +29,7 @@ cat prog.c | ./prog           # Print garbage: might mess up your terminal
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

2018/anderson/README.md

@@ -15,7 +15,7 @@ code](#alternate-code) below for more details.
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

2018/bellard/README.md

@@ -15,7 +15,7 @@ code](#alternate-code) below.
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 eog lena.ppm # On Linux

2018/burton1/README.md

@@ -15,7 +15,7 @@ code](#alternate-code) below.
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

2018/burton2/README.md

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

2018/ciura/README.md

@@ -16,7 +16,7 @@ below for more details.
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./prog < Makefile

2018/endoh1/README.md

@@ -12,7 +12,7 @@ make
 ```
 
 
-### Try:
+## Try:
 
 To see the input files and feed them to the program, redirecting to GIF files:
 

2018/endoh2/README.md

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

2018/ferguson/README.md

@@ -15,7 +15,7 @@ monkey Eric. See [Alternate code](#alternate-code) below.
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

2018/giles/README.md

@@ -16,7 +16,7 @@ make
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./prog ioccc.txt

2018/hou/README.md

@@ -25,7 +25,7 @@ For more detailed information see [2018 hou in bugs.md](/bugs.md#2018-hou).
 View `output.html` in a browser.
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

2018/mills/README.md

@@ -36,7 +36,7 @@ For more detailed information see [2018 mills in bugs.md](/bugs.md#2018-mills).
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./prog

2018/poikola/README.md

@@ -12,7 +12,7 @@ make
 ```
 
 
-### Try:
+## Try:
 
 On a terminal that supports 24 bit color, has black background, and size at
 least 125x38, try:

2018/vokes/README.md

@@ -23,7 +23,7 @@ For more detailed information see [2018 vokes in bugs.md](/bugs.md#2018-vokes).
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh

2018/yang/README.md

@@ -17,7 +17,7 @@ less generated3.c
 ```
 
 
-### Try:
+## Try:
 
 ```sh
 ./try.sh