Update Canvas API TOS link
Update Canvas API TOS link

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Test plan:
- Run the "rails doc:api" to rebuild api docs
- visit <local canvas>/doc/api/index.html and verify
  the link to the API TOS now works.

Change-Id: I7fc22f8648453940d2e420f65ce0f1ded741b9ac
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/279141
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
QA-Review: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
Product-Review: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms