Preparation for 1.5.0 Release

[markmandel]

Also snuck in a grammer issue in the release.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: markmandel, pooneh-m

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[agones-bot]

Build Succeeded 👏

Build Id: 4244dccf-d537-47d8-9078-42745661ce38

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

• image: gcr.io/agones-images/agones-controller:1.5.0-0b63bd3
• image: gcr.io/agones-images/agones-sdk:1.5.0-0b63bd3
• image: gcr.io/agones-images/agones-ping:1.5.0-0b63bd3
• Linux C++ SDK (build): agonessdk-1.5.0-0b63bd3-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.5.0-0b63bd3.zip

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

• https://0b63bd3-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1391/head:pr_1391 && git checkout pr_1391
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.5.0-0b63bd3