added support for graph-video url

[zoharbabin]

for some reason, the new v4 SDK dropped support for the different API sub domains... which meant that video publishing would use the main api rather than the graph-video subdomain.
This minor fix introduces a change to support the video url.

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[SammyK]

This is a good first step, but depending on the HTTP client you're using you'll get different results.

• Files need to be posted as multipart/form-data
  • For curl implementations, you'll need to make use of CURLFile class to get the proper encoding.
  • Stream wrappers will break because they always assume application/x-www-form-urlencoded encoding.
  • Guzzle should be able to detect the encoding properly if I remember correctly. You might have to explicitly define multipart/form-data though.
• The timeouts of 60 seconds are far too low for video uploads. This would need to be updated on all the HTTP client implementations.

Feel free to port over any of the code from #279 which added file upload support to 4.1.

[gfosco]

I don't mind adding this to 4.0, especially since 4.1 isn't released yet.. If the naive approach here doesn't work, for the reasons Sammy mentions, then 4.1 is the answer.