fixed calculation of messageLength.

Otherwise e.g "08" will be parsed as octal 8 instead of the needed string representation. see https://github.com/Atmosphere/atmosphere-javascript/commit/6d2d27ff7b11693f3e37c9bc774be87f271786be#commitcomment-3426339
Merge pull request #2 from staabm/patch-1

fixed calculation of messageLength.