Add assertion utility to test for a gzipped buffer

[ShraddheyaS]

Resolves #158.

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Description

What is the purpose of this pull request?

This pull request:

• Adds assertion utility to test for a gzipped buffer

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves RFC: add assertion utility to test for a gzipped buffer #158

Questions

Any questions for reviewers of this pull request?

Is there a better way of testing? Somehow using actual gzipped files?

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

No.

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@stdlib-js/reviewers

[kgryte]

LGTM. Will make some minor changes on my end.