docs(displayfile): escape ! from the subject example command

subjects/displayfile/README.md

@@ -9,7 +9,7 @@ Write a program that displays, on the standard output, the content of a file giv
 ```console
 $ go run .
 File name missing
-$ echo "Almost there!!" > quest8.txt
+$ echo 'Almost there!!' > quest8.txt
 $ go run . quest8.txt main.go
 Too many arguments
 $ go run . quest8.txt