Call constructor's .parse call in nextTick 

As stated on #35 there was a problem with using 'hand-made' Readable streams in Node v0.10.30. For more description about the problem, see https://github.com/cirocosta/gulp-converter-tjs/issues/3

--

This PR also adds a test for this and bumps node-expat version so that it works for node v0.11.x environments.