fix URLs in variable substitution files
fix URLs in variable substitution files

Then we don't all keep getting tools_variable_substitutions.md
shown as checked out all the time.

CLOSES: DOC-1235
flag=none

Test plan:
- jenkins passes

Change-Id: If5a093ed006a534262ba48138013acc4e769491b
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/245638
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Alex Anderson <8690c85fe64134788579ce84d396a27368e019d5@instructure.com>
QA-Review: James Williams <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
Product-Review: James Williams <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

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