add quotes around canvas in API doc

To make it more clear that the word "cavnas" has to be passed
explicitly for the users to be notified for password setup.

closes FOO-3948
flag=none

test plan:
- generate API docs
- go to SIS Import Format Documentation
- make sure the word canvas has quotes around it in
  canvas_password_notifcation description of users.csv

Change-Id: Ifc701c181efbf8fc4b59b6b5eabd9e5a1ba0e2c1
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/333482
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Ajmal Esa <ajmal.esa@instructure.com>
Product-Review: Ajmal Esa <ajmal.esa@instructure.com>
Reviewed-by: Michael Hulse <michael.hulse@instructure.com>

doc/api/sis_csv.md

@@ -293,7 +293,7 @@ declared user type from the user.</td>
 <td></td>
 <td></td>
 <td>Defaults to false. When true, user is notified for password setup if
-the authentication_provider_id is canvas</td>
+the authentication_provider_id is "canvas"</td>
 </tr>
 <tr>
 <td>home_account</td>