Bug in RecordWin method on FileSystemPlayerStore

[MaT1g3R]

On the last line of RecordWin, if you write f.database.Encode(league), scores for new players are not correctly persisted, but no tests will catch this error. Adding the below test will catch this bug:

	t.Run("wins for new players are persisted", func(t *testing.T) {
		database, cleanDatabase := createTempFile(t, `[
        {"Name": "Cleo", "Wins": 10},
        {"Name": "Chris", "Wins": 33}]`)
		defer cleanDatabase()

		store, err := NewFileSystemPlayerStore(database)
		AssertNoError(t, err)

		store.RecordWin("Pepper")

		store, err = NewFileSystemPlayerStore(database)
		AssertNoError(t, err)

		got := store.GetPlayerScore("Pepper")
		want := 1
		AssertScoreEquals(t, got, want)
	})