Update README.md

subjects/swapname/README.md

@@ -4,7 +4,7 @@
 
 Write a program that takes two words in the first argument and swaps them.
 - If the number of arguments is not 2, nothing should be printed.
-- If the first argument is not a string, the program should print `"Error\n"`.
+- If the first argument is not an alphanumeric characters, the program should print `"Error\n"`.
 - Skip the spaces in the first of the two words.
 - Print the result with a new line at the end (`'\n'`).
 
@@ -23,4 +23,4 @@ $ go run . "Hello World   " | cat -e
 Error$
 $ go run . "Hello World Hello" | cat -e
 Error$
-```
+```