Rp should not auto close rtc.

Update parser to follow HTML5 spec change at:
https://github.com/w3c/html/commit/c61397b989b28235ee2228f280aa8d475f3b9ebf

I sent pull request of test case at:
https://github.com/darobin/html5lib-tests/pull/2

Note that in my environment there is 29 test failure with the combination this new-ruby branch and html5lib-test's new-ruby branch. I confirmed that this change did not add test failure.