Updated Embed.php to use correct DocTypes

[StevenWillett]

I have forked and updated the Embed.php file to use correct DocTypes and includes use case that was also missing.

Tried to create pull request, but not able, possibly disabled :)

See fork here: https://github.com/StevenWillett/metabase-php

Hope this helps others.

[ipeevski]

Hey Steven, thanks for your contribution.
Let's try to figure out how to do the pull request so it keeps your attribution. I haven't disabled anything and can't seem to find an option about it. How did you try to do it?

[ipeevski]

I figured it out. Pull requested and merged :)