Update requests to 2.20.0

[pyup-bot]

This PR updates requests[security] from 2.18.4 to 2.20.0.

Changelog

2.20.0

-------------------

**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

-------------------

**Bugfixes**

-   Fixed issue where status\_codes.py's `init` function failed trying
 to append to a `__doc__` value of `None`.

2.19.0

-------------------

**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.
-   Fixed issue where loading the default certificate bundle from a zip
 archive would raise an `IOError`.
-   Fixed issue with unexpected `ImportError` on windows system which do
 not support `winreg` module.
-   DNS resolution in proxy bypass no longer includes the username and
 password in the request. This also fixes the issue of DNS queries
 failing on macOS.
-   Properly normalize adapter prefixes for url comparison.
-   Passing `None` as a file pointer to the `files` param no longer
 raises an exception.
-   Calling `copy` on a `RequestsCookieJar` will now preserve the cookie
 policy correctly.

**Dependencies**

-   We now support idna v2.7.
-   We now support urllib3 v1.23.

Links

• PyPI: https://pypi.org/project/requests
• Changelog: https://pyup.io/changelogs/requests/
• Homepage: http://python-requests.org