Properly JSON-stingify move before broadcasting it

Properly JSON-stingify move before broadcasting it

With the Tic Tac Toe game, this bug was hidden, (since the move data
is just an integer and there's no difference in strignifying that or
not). But an upcoming game (Scribe) uses a pair of integers, and
there's a lot of difference between "1,2" and "[1,2]" since only the
latter is proper JSON.