Update dependency for Kubeclient::Config vulnerability

[cben]

Proposed changes

See ManageIQ/kubeclient#554, I fixed an embarrasing vulnerability in Kubeclient::Config — it could wrongly set VERIFY_NONE, allowing man-in-the-middle attacks and stealing cluster credentials 😳
And I see this repo does use Kubeclient::Config.read.

kubeclient generally obeys SemVer, so upgrading 4.6.z to 4.9.z should be safe. OTOH if you think upgrading is tricky, let us know on that kubeclient issue, we can backport the fix!

@harshit-splunk @rockb1017 I see several of fluent-plugin-* gems depend on '~> 4.6.0', and more than one are maintained by Splunk — I'm not going to send PRs to them all, please spread the word.

Types of changes

What types of changes does your code introduce?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue) — BUT I DID NOT TEST THIS
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING doc
• I have read the CLA
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules