update example solution

Author: AlvesJorge

exercises/concept/football-match-reports/.meta/src/reference/java/FootballMatchReports.java

@@ -30,7 +30,7 @@ public static String onField(int shirtNum) {
                 playerDescription = "striker";
                 break;
             default:
-                throw new IllegalArgumentException();
+                playerDescription = "unknown";
         }
         return playerDescription;
     }