Updating hackney's version in dependencies

[raspberry-lef]

Hello, @KazuCocoa, thank you for your work on http_proxy.

Trying out http_proxy on a fresh Phoenix project seems to require the following downgrades because of the {:hackney, "1.6.5"} dependency:

certifi 2.6.1 => 0.7.0 (major) idna 6.1.1 => 1.2.0 (major) mimerl 1.2.0 => 1.0.2 ssl_verify_fun 1.1.6 => 1.1.1

hackney is currently at version 1.17.4. Perhaps it would be worth considering to update the dependency on hackney to ~> 1.17 for a new release of http_proxy which you could also tag on here (because v1.31.1 appears as the latest on GitHub while in reality v1.5.0 is out). :-)

Thank you