Fixed broken link to pass tests.

[devloop0]

What type of PR is this?
/kind bug

What this PR does / Why we need it:
Fixes a broken link in a markdown file so that make test passes.

Which issue(s) this PR fixes:

Closes #

Special notes for your reviewer:

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[devloop0]

@googlebot I signed it!

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[markmandel]

Nice one!

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: devloop0, markmandel

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[agones-bot]

Build Succeeded 👏

Build Id: dbe05076-5b44-4529-a1cc-ce56b305f8f6

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.7.0-b84fed7
• image: gcr.io/agones-images/agones-sdk:1.7.0-b84fed7
• image: gcr.io/agones-images/agones-ping:1.7.0-b84fed7
• Linux C++ SDK (build): agonessdk-1.7.0-b84fed7-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.7.0-b84fed7.zip

A preview of the website (the last 30 builds are retained):

• https://b84fed7-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/1633/head:pr_1633 && git checkout pr_1633
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.7.0-b84fed7