Fix definitions for DOM interface

[danjohnso]

DOM interfaces were off slightly from published API. Adjusted them so TS users can use accurately

I understand that:

• I'm submitting this PR for reference only. It shows an example of what I'd like to see changed but
  I understand that it will not be merged and I will not be listed as a contributor on this project.

[danjohnso]

I am a typescript user and looking to use some of the SVG APIs in my project. I noticed the definitions are off from your actual API. I didn't review all of your interfaces, but DOM ones were quick fixes since I need them in m y project. I am shimming my project with these definitions, but thoughts others may end up in the same boat.

[tagliala]

Hi!

Thanks for this PR.

I've assigned @mlwilkerson so he can take a look

[danjohnso]

Any chance this is going to get merged?