bugfix: regex not instantiated where intended

var chess = new Chess();
chess.move({from: 'e2', to: 'e4'});
var pgn = chess.pgn({max_width: 5, newline_char: \n});
// output:
// [White "carolyn"]
// [Black "hippo"]
// [Date "2014-1-18"]
// 
// 1. e4

var chessB = new Chess();
chessB.load_pgn(pgn);

// BUG HERE:
chessB.pgn({max_width: 5, newline_char: \n});
// outputs: [[White "carolyn"] [Black "hippo"] [Date "2014-1-18"] "[White "carolyn"] [Black "hippo"] [Date "2014-1-18"]"]  1. e4
issue(#51): test to cover double-header writing bug.
issue(#51): making use of updated `mask` when building RegExp for "newline_char" option.
Merge pull request #52 from jzacsh/master

fix for issue(#51) - writing double `[[headers "foo"] headers "foo"]`