Site->Follow typo: replace `_sid` with `_id`
Site->Follow typo: replace `_sid` with `_id`

`_sid` is the wrong variable, and it was incorrectly called for when
moving `Follow()` with the previous commits.

DNESS/wpcom.js,Automattic/wpcom.js,dnessorga/wpcom.js,dnessorga/wpcom.js,Automattic/wpcom.js,DNESS/wpcom.js