Fix HTTP regex not matching with Http

[knottnt]

Issue #, if available: 2221

Description of changes:

• Update HTTP regex to only match if not followed by an "S" and additional capital letter and Http to only match if not followed by "s".
• Add additional test cases for common HTTP related field names.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ack-prow]

@knottnt: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
verify-attribution	2f89dc3	link	false	/test verify-attribution

Full PR test history. Your PR dashboard.

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[jaypipes]

Nice catch! :)

[ack-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jaypipes, knottnt

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