force navigation tabs cache to invalidate when changing external tools

fixes:PLAT-277

test plan:
1. Go to https://www.eduappcenter.com/apps/redirect
2. Enter criteria for a redirect link configuration URL
3. Access an account in Canvas
4. Add the Redirect External Tool with your configuration URL
5. Observe link is added to your Navigation per your settings
6. Attempt to edit the External Tool in Canvas with a new configuration URL you get from https://www.eduappcenter.com/apps/redirect after putting in new data
7. Observe that changes are reflected in the External Tools tab but the actual link in Navigation menus is changed

Change-Id: I2b233cb89e4b446cd66b6e826ec8de894a02bfdd
Reviewed-on: https://gerrit.instructure.com/33757
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
Reviewed-by: Eric Berry <ericb@instructure.com>
Product-Review: Nathan Mills <nathanm@instructure.com>