Add update_video method

[kangkyu]

• Rearrange files
• Use convert_keys

[kangkyu]

Possible to do something like this:

u = Fb::User.new(access_token: "EAAH...ZDZD")
p = u.pages.first
p.update_video("1839018720192906", name: "Hello, Gapbun", description: "Description updated")