Pin the postcss-cli version

[markmandel]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking

/kind bug

/kind cleanup
/kind documentation
/kind feature
/kind hotfix

What this PR does / Why we need it:

This fixes a break in CI. postcss-cli@8.3.1 broke something in hugo, so we'll pin the version, which fixes things and allows CI to run again! 🙌

Which issue(s) this PR fixes:

N/A

Special notes for your reviewer:

N/A

[agones-bot]

Build Succeeded 👏

Build Id: 7ca70dbc-35c0-4c9c-afc6-0d6b65d980cf

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

• image: gcr.io/agones-images/agones-controller:1.11.0-8c05616
• image: gcr.io/agones-images/agones-sdk:1.11.0-8c05616
• image: gcr.io/agones-images/agones-ping:1.11.0-8c05616
• Linux C++ SDK (build): agonessdk-1.11.0-8c05616-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.11.0-8c05616.zip

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

• https://8c05616-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/1930/head:pr_1930 && git checkout pr_1930
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.11.0-8c05616

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [markmandel,roberthbailey]

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