Update 018_functions.zig

exercises/018_functions.zig

@@ -1,6 +1,6 @@
 //
 // Functions! We've already created lots of functions called "main()". Now let's
-// try writing one of our own:
+// do something different:
 //
 //     fn foo(n: u8) u8 {
 //         return n + 1;