twelve-days: update starter implementation to match POLICIES.md

exercises/twelve-days/src/main/java/TwelveDays.java

 public class TwelveDays {
-	public String verse(int verseNumber) {
-		throw new UnsupportedOperationException("Delete this statement and provide your own implementation.");
-	}
-}
+    public String verse(int verseNumber) {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+
+    public String verses(int startVerse, int endVerse) {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+}

exercises/twelve-days/src/test/java/TwelveDaysTest.java

     @Ignore("Remove to run test")
     @Test
     public void testMultipleVerses() {
-/*
         String expectedVerseOneToThree = "On the first day of Christmas my true love gave to me, " +
                 "a Partridge in a Pear Tree.\n\n" +
                 "On the second day of Christmas my true love gave to me, two Turtle Doves, " +
                 "On the third day of Christmas my true love gave to me, three French Hens, two Turtle Doves, " +
                 "and a Partridge in a Pear Tree.\n";
         assertEquals(expectedVerseOneToThree, twelveDays.verses(1, 3));
-*/
     }
 
     @Ignore("Remove to run test")
     @Test
     public void testSingWholeSong() {
-/*
         String expectedSong = "On the first day of Christmas my true love gave to me, a Partridge in a Pear Tree.\n" +
                 "\n" +
                 "On the second day of Christmas my true love gave to me, two Turtle Doves, " +
                 "seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, " +
                 "three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.\n";
         assertEquals(expectedSong, twelveDays.sing());
-*/
     }
 }