Update hackney requirement from 1.6.5 to 1.15.2

[dependabot[bot]]

Updates the requirements on hackney to permit the latest version.

Changelog

Sourced from hackney's changelog.

1.15.2 - 2019-09-25

• doc: fix test run example in readme
• fix: hackney stream, send hackney_response before calling handle_error
• fix: error remove ssl honor_cipher_order option
• doc: document self-signed certificate usage
• bump ssl_verify_fun to 1.1.5
• fix: don't use default pool if set to false
• fix: hackney_headers_new:store/3 fix value appending to a list
• fix: miscellaneous specs
• doc: miscellaneous improvements

1.15.1 - 2019-02-26

• fix: don't try to encode to IDN with full ASCII names.

this behaviour is similar to curl and fix errors some people had with docker creating domain names containing a _

• doc: clarify recv_timeout usage
• fix: don't try to encode hostname IPs to IDN
• fix: path encoding to support ( ) characters
• bump mimerl to 1.2
• bump certifi to 2.5.1

1.15.0 - 2019-01-04

• improve multipart: send form with a field names for files
• fix pool checkout_cancel: reduce the number of pending requests

1.14.3 - 2018-09-29

• idna: don't try to encode a unix socket path

1.14.2 - 2018-09-28

• fix: don't IDNA encode the host with unix scheme
• doc: document basic_auth setting

1.14.0 - 2018-09-12

• bump to certifi 2.4.2

... (truncated)

Commits

• 3c32f04 remove deprecated MAINTAINERS metadata
• e6b3264 bump to 1.15.2
• e8bbfc8 Fixes test run example
• 18723ef Use spaces (#586)
• b4a48ed Send hackney_response before calling handle_error (#573)
• 9c3f578 Fix error caused by honor_cipher_order, CI errors (#589)
• b3ea4ea document self-signed certificate usage (#578)
• dbc1249 improve docs and type spec (#579)
• 2a217e4 hackney.POOLNAME.free_count is actually histogram (#582)
• 4f1079a bump ssl_verify_fun to 1.1.5 (#575)
• Additional commits viewable in compare view

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