Misprints in README.md (showLeaderboard and signout)

[Samleo8]

There are 2 misprints in the README.md:

1. Sign Out
googleplaygame.signout(); should be googleplaygame.signOut();
2. Show Leaderboards
var data = { leaderboardId: "board1" }; googleplaygame.showLeaderboard(leaderboardId);

should be

var data = { leaderboardId: "board1" }; googleplaygame.showLeaderboard(data);

#14