go-counting: use provided enumeration instead of Strings

Use of enumeration should be consistent across the test suite.

exercises/go-counting/src/test/java/GoCountingTest.java

 	public void oneTerritoryIsWholeBoardTest() {
 		GoCounting gocounting = new GoCounting(" ");
 		
-		HashMap<String, Set<Point>> territories = new HashMap<>();
+		HashMap<Player, Set<Point>> territories = new HashMap<>();
 		Set<Point> blackTerritory = new HashSet<>();
 		Set<Point> whiteTerritory = new HashSet<>();
 		Set<Point> noneTerritory = new HashSet<>();
 		noneTerritory.add(new Point(0, 0));
 		
-		territories.put("BLACK", blackTerritory);
-		territories.put("WHITE", whiteTerritory);
-		territories.put("NONE", noneTerritory);
+		territories.put(Player.BLACK, blackTerritory);
+		territories.put(Player.WHITE, whiteTerritory);
+		territories.put(Player.NONE, noneTerritory);
 		
 		assertEquals(territories, gocounting.getTerritories());
 	}
 		
 		Set<Point> noneTerritory = new HashSet<>();
 		
-		HashMap<String, Set<Point>> territories = new HashMap<>();
-		territories.put("BLACK", blackTerritory);
-		territories.put("WHITE", whiteTerritory);
-		territories.put("NONE", noneTerritory);
+		HashMap<Player, Set<Point>> territories = new HashMap<>();
+		territories.put(Player.BLACK, blackTerritory);
+		territories.put(Player.WHITE, whiteTerritory);
+		territories.put(Player.NONE, noneTerritory);
 		
 		assertEquals(territories, gocounting.getTerritories());
 	}
 	public void twoRegionRectangularBoardTest() {
 		GoCounting gocounting = new GoCounting(" B ");
 		
-		HashMap<String, Set<Point>> territories = new HashMap<>();
+		HashMap<Player, Set<Point>> territories = new HashMap<>();
 		Set<Point> blackTerritory = new HashSet<>();
 		blackTerritory.add(new Point(0, 0));
 		blackTerritory.add(new Point(2, 0));
 		Set<Point> whiteTerritory = new HashSet<>();
 		Set<Point> noneTerritory = new HashSet<>();
 		
-		territories.put("BLACK", blackTerritory);
-		territories.put("WHITE", whiteTerritory);
-		territories.put("NONE", noneTerritory);
+		territories.put(Player.BLACK, blackTerritory);
+		territories.put(Player.WHITE, whiteTerritory);
+		territories.put(Player.NONE, noneTerritory);
 		
 		assertEquals(territories, gocounting.getTerritories());
 	}