fix: address eslint issues in postman tests

[brownoxford]

Address disabled eslint rules from #44.

Note that the eslint-disable-line import/extensions exception when importing the sha256 module is required because the default specifier resolution of "explicit" will not locate the module without the .js extension. An alternative would be to require --experimental-specifier-resolution=node on the command line when running the tests, but that seems like an unnecessary barrier to testing.

[mkhraisha]

is there a specific reason we switched out from using async/await to .then?

[brownoxford]

is there a specific reason we switched out from using async/await to .then?

These were refactored to comply with the new eslint rules. Using await inside of a loop violates Disallow await inside of loops (no-await-in-loop)