Capitalize "GitHub" correctly throughout the docs

[hegemonic]

I originally noticed this issue in the https://agones.dev/ top navbar.

[hegemonic]

Apologies for the multiple commits. If you need me to squash them on my end, please let me know.

[agones-bot]

Build Failed 😱

Build Id: acb1a5d6-bae9-498e-b813-bcb99d71c56f

• Cloud Build view
• Cloud Build log download

To get permission to view the Cloud Build view, join the agones-discuss Google Group.

[roberthbailey]

Apologies for the multiple commits. If you need me to squash them on my end, please let me know.

The PR will be automatically squashed when it gets merged.

[agones-bot]

Build Failed 😱

Build Id: 7fe40c61-435e-4e69-83c8-52194af51371

• Cloud Build view
• Cloud Build log download

To get permission to view the Cloud Build view, join the agones-discuss Google Group.

[agones-bot]

Build Failed 😱

Build Id: 8f623608-000b-46ac-8865-86b890970e95

• Cloud Build view
• Cloud Build log download

To get permission to view the Cloud Build view, join the agones-discuss Google Group.

[agones-bot]

Build Failed 😱

Build Id: cac94f11-bb76-4a59-b42f-ec6e7c2818c5

• Cloud Build view
• Cloud Build log download

To get permission to view the Cloud Build view, join the agones-discuss Google Group.

[agones-bot]

Build Succeeded 👏

Build Id: ff355fd8-c635-47ae-bee5-9e208f618c6d

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

• image: gcr.io/agones-images/agones-controller:1.0.0-5c2bff3
• image: gcr.io/agones-images/agones-sdk:1.0.0-5c2bff3
• image: gcr.io/agones-images/agones-ping:1.0.0-5c2bff3
• Linux C++ SDK (build): agonessdk-1.0.0-5c2bff3-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.0.0-5c2bff3.zip

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

• https://5c2bff3-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/990/head:pr_990 && git checkout pr_990
• helm install install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.0.0-5c2bff3