Several broken links on the sponsors page

[yatil]

Edit here: https://github.com/w3c/wai-about-wai/edit/master/_about/sponsoring.md

• US Department of Health and Human Services, National Institute for Disability, Independent Living and Rehabilitation Research,
• US Department of Health and Human Services (previously US Department of Education) National Institute on Disability, Independent Living, and Rehabilitation Research, contract EDOSE10C0067
• Assistive Devices Industry Office, Industry Canada, Government of Canada
• Verizon Foundation