Update the TMSS API document url on _data/api-list.yml.

[NairChandu]

Looks like we have overlooked the url on #739 and incorrectly updated the API document url. It's supposed to be https://open.gsa.gov/api/ratequeryhhg/ on line number 93 of _data/api-list.yml.

[vickimcfadden]

@NairChandu the TMSS API appears to be working now. Can this issue be closed or is an update still needed?