Fix istio sds link in installing istio

[mpetason]

Fixes #2228

Proposed Changes

• Changed capitalized SDS to lowercase sds so the link will work

[knative-prow-robot]

Hi @mpetason. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[evankanderson]

/lgtm
/approve

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: evankanderson, mpetason

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[knative-prow-robot]

@mpetason: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-knative-docs-markdown-link-check	f0775d4	link	/test pull-knative-docs-markdown-link-check

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.