Edit the name of the third-party-requests ml

We created a new mailing list for third party gerrit account
requests. We called the mailing list third-party-request. This
is a problem since the mail server uses -request as a reserved
word. This patch edits the documentation to the renamed mailing
list name, third-party-requests.

Change-Id: I489b4fc8472aeef2a1eb2c3b5fe2590ae9d31534
Merge "Edit the name of the third-party-requests ml"