[Fixes #382] Correct endpoint for single spam report requests

[bermannoah]

Fixes #382

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

Updates the single spam report retrieval and deletion endpoints to be in line with the base API. https://sendgrid.com/docs/API_Reference/Web_API_v3/spam_reports.html#Get-a-specific-spam-report-GET and also updates the License dates.

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

Hello @bermannoah,

Thanks again for the PR!

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[bermannoah]

Hello @thinkingserious -- thanks for the quick merge! Glad I could help. :-)