update manuscript

manuscript/chapter16.txt

@@ -113,10 +113,7 @@ f()for i in "$@"; do echo "$i"; done
 
 ## Simpler `case` statement to set variable
 
-We can use the `:` builtin to avoid repeating `variable=` in a case
-statement. The `$_` variable stores the last argument of the last
-successful command. `:` always succeeds so we can abuse it to store the
-variable value.
+The `:` built-in can be used to avoid repeating `variable=` in a case statement. The `$_` variable stores the last argument of the last command. `:` always succeeds so it can be used to store the variable value.
 
 ```shell
 # Modified snippet from Neofetch.