[Security] Bump requests from 2.2.1 to 2.20.0 in /requirements

[dependabot-preview]

Bumps requests from 2.2.1 to 2.20.0. This update includes security fixes.

Vulnerabilities fixed

Sourced from The GitHub Security Advisory Database.

Moderate severity vulnerability that affects requests
The Requests package through 2.19.1 before 2018-09-14 for Python sends an HTTP Authorization header to an http URI upon receiving a same-hostname https-to-http redirect, which makes it easier for remote attackers to discover credentials by sniffing the network.

Affected versions: <= 2.19.1

Changelog

Sourced from requests's changelog.

2.20.0 (2018-10-18)

Bugfixes

• Content-Type header parsing is now case-insensitive (e.g.
  charset=utf8 v Charset=utf8).
• Fixed exception leak where certain redirect urls would raise
  uncaught urllib3 exceptions.
• Requests removes Authorization header from requests redirected
  from https to http on the same hostname. (CVE-2018-18074)
• should_bypass_proxies now handles URIs without hostnames (e.g.
  files).

Dependencies

• Requests now supports urllib3 v1.24.

Deprecations

• Requests has officially stopped support for Python 2.6.

2.19.1 (2018-06-14)

Bugfixes

• Fixed issue where status_codes.py's init function failed trying
  to append to a __doc__ value of None.

2.19.0 (2018-06-12)

Improvements

• Warn user about possible slowdown when using cryptography version
  < 1.3.4
• Check for invalid host in proxy URL, before forwarding request to
  adapter.
• Fragments are now properly maintained across redirects. (RFC7231
  7.1.2)
• Removed use of cgi module to expedite library load time.
• Added support for SHA-256 and SHA-512 digest auth algorithms.
• Minor performance improvement to Request.content.
• Migrate to using collections.abc for 3.7 compatibility.

Bugfixes

• Parsing empty Link headers with parse_header_links() no longer
  return one bogus entry.

... (truncated)

Commits

• bd84045 v2.20.0
• 7fd9267 remove final remnants from 2.6
• 6ae8a21 Add myself to AUTHORS
• 89ab030 Use comprehensions whenever possible
• 2c6a842 Merge pull request #4827 from webmaven/patch-1
• 30be889 CVE URLs update: www sub-subdomain no longer valid
• a6cd380 Merge pull request #4765 from requests/encapsulate_urllib3_exc
• bbdbcc8 wrap url parsing exceptions from urllib3's PoolManager
• ff0c325 Merge pull request #4805 from jdufresne/https
• b0ad249 Prefer https:// for URLs throughout project
• Additional commits viewable in compare view

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot merge will merge this PR after your CI passes on it
• @dependabot squash and merge will squash and merge this PR after your CI passes on it
• @dependabot cancel merge will cancel a previously requested merge and block automerging
• @dependabot reopen will reopen this PR if it is closed
• @dependabot ignore this [patch|minor|major] version will close this PR and stop Dependabot creating any more for this minor/major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)
• @dependabot use these labels will set the current labels as the default for future PRs for this repo and language
• @dependabot use these reviewers will set the current reviewers as the default for future PRs for this repo and language
• @dependabot use these assignees will set the current assignees as the default for future PRs for this repo and language
• @dependabot use this milestone will set the current milestone as the default for future PRs for this repo and language
• @dependabot badge me will comment on this PR with code to add a "Dependabot enabled" badge to your readme

Additionally, you can set the following in your Dependabot dashboard:

• Update frequency (including time of day and day of week)
• Automerge options (never/patch/minor, and dev/runtime dependencies)
• Pull request limits (per update run and/or open at any time)
• Out-of-range updates (receive only lockfile updates, if desired)
• Security updates (receive only security updates, if desired)

Finally, you can contact us by mentioning @dependabot.