Bug fix for Ruby version of Checkers

We were using the result of Board.make_move!() to determine whether
the current player could jump again.  This worked by accident but was
not part of the specified interface.

I've changed the code to ignore the return value and instead query the
move object itself.

23_Checkers/ruby/checkers.rb

@@ -139,10 +139,10 @@ def my_turn(board, jumpStart = nil)
 
   # Do the move
   puts "My move: #{bestMove}"
-  canMoveAgain = board.make_move!(bestMove)
+  board.make_move!(bestMove)
 
   # Repeat (recursively) if we can make another jump
-  my_turn(board, bestMove.to) if canMoveAgain
+  my_turn(board, bestMove.to) if bestMove.jump?
 
   # No loss yet!
   return true
@@ -182,8 +182,8 @@ def players_turn(board)
     return false    if !from && !move
     return true     if from && !move
 
-    canMoveAgain = board.make_move!(move)
-    return true unless canMoveAgain
+    board.make_move!(move)
+    return true unless move.jump?
 
     # If the player can jump again, repeat from the new position.
     from = move.to