Fix typo in Makefile

[orthros]

environemt -> environment

[agones-bot]

Build Succeeded 👏

Build Id: 68b3b9ab-44fe-4f61-b5a9-4eff5a138b14

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

• image: gcr.io/agones-images/agones-controller:1.0.0-f11b52e
• image: gcr.io/agones-images/agones-sdk:1.0.0-f11b52e
• image: gcr.io/agones-images/agones-ping:1.0.0-f11b52e
• Linux C++ SDK (build): agonessdk-1.0.0-f11b52e-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.0.0-f11b52e.zip

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

• https://f11b52e-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1021/head:pr_1021 && git checkout pr_1021
• helm install install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.0.0-f11b52e

[google-oss-robot]

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