Correct syntax error in select.md (#745)

In the previous section, an error return was added to the `Racer()` function. In the text underneath this code block, there is a note that says. 

"Note that we've also handled the error return in our original text, we're using `_` for now to ensure the tests will run.

I think the error was not actually ignored with an underscore as you intended.

Author: kevinlangmade

select.md

@@ -269,7 +269,7 @@ func TestRacer(t *testing.T) {
 		fastURL := fastServer.URL
 
 		want := fastURL
-		got, err := Racer(slowURL, fastURL)
+		got, _ := Racer(slowURL, fastURL)
 
 		if got != want {
 			t.Errorf("got %q, want %q", got, want)