[update] Scheduled weekly dependency update for week 18

Created by: pyup-bot

Updates

Here's a list of all the updates bundled in this pull request. I've added some links to make it easier for you to find all the information you need.

Pillow	4.1.0	»	4.1.1	PyPI | Changelog | Homepage
urllib3	1.21	»	1.21.1	PyPI | Changelog | Docs

Changelogs

urllib3 1.21 -> 1.21.1

1.21.1

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• Fixed SecureTransport issue that would cause long delays in response body delivery. (Pull 1154)

• Fixed regression in 1.21 that threw exceptions when users passed the socket_options flag to the PoolManager. (Issue 1165)

• Fixed regression in 1.21 that threw exceptions when users passed the assert_hostname or assert_fingerprint flag to the PoolManager. (Pull 1157)

That's it for now!

Happy merging! 🤖