Update kubergrunt ver in readme

[pras111gw]

Describe the bug Readme's install guide has a reference to deprecated kubergrunt version v0.5.13. Update it to a recent release

To Reproduce Steps to reproduce the behavior including the relevant Terraform/Terragrunt/Packer version number and any code snippets and module inputs you used.

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Expected behavior A clear and concise description of what you expected to happen.

Nice to have

• [ ] Terminal output
• [x] Screenshots

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