[FileAPI] Switch all links towards tools.ietf.org to HTTPS (#3)

I checked that all of them were actually sourced as HTTPS by https://labs.w3.org/specrefs/bibrefs?refs=rfcXXXX
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/FileAPI/pull/3

-- Commit Summary --

  * Switch all links towards tools.ietf.org to HTTPS

-- File Changes --

    M index.html (26)

-- Patch Links --

https://github.com/w3c/FileAPI/pull/3.patch
https://github.com/w3c/FileAPI/pull/3.diff

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