Update pillow to 4.2.1

[pyup-bot]

There's a new version of Pillow available.
You are currently using 4.1.1. I have updated it to 4.2.1

These links might come in handy: PyPI | Changelog | Homepage

Changelog

4.2.1

---

• CI: Fix version specification and test on CI for PyPy/Windows 2608
  [wiredfool]

4.2.0

---

• Doc: Clarified Image.save:append_images documentation 2604
  [radarhere]

• CI: Amazon Linux and Centos6 docker images added to TravisCI 2585
  [wiredfool]

• Image.alpha_composite added 2595
  [wiredfool]

• Complex Text Support 2576
  [ShamsaHamed, Fahad-Alsaidi, wiredfool]

• Added threshold parameter to ImageDraw.floodfill 2599
  [nediamond]

• Added dBATCH parameter to ghostscript command 2588
  [radarhere]

• JPEG: Adjust buffer size when icc_profile > MAXBLOCK 2596
  [Darou]

• Specify Pillow Version in one place 2517
  [wiredfool]

• CI: Change the owner of the TRAVIS_BUILD_DIR, fixing broken docker runs 2587
  [wiredfool]

• Fix truncated PNG loading for some images, Fix memory leak on truncated PNG images. 2541, 2598
  [homm]

• Add decompression bomb check to Image.crop 2410
  [wiredfool]

• ImageFile: Ensure that the err_code variable is initialized in case of exception. 2363
  [alexkiro]

• Tiff: Support append_images for saving multipage TIFFs 2406
  [blochl]

• Doc: Clarify that draft is only implemented for JPEG and PCD 2409
  [wiredfool]

• Test: MicImagePlugin 2447
  [hugovk]

• Use round() instead of floor() to eliminate zero coefficients in resample 2558
  [homm]

• Remove deprecated code 2549
  [hugovk]

• Added append_images to PDF saving 2526
  [radarhere]

• Remove unused function core image function new_array 2548
  [hugovk]

• Remove unnecessary calls to dict.keys() 2551
  [jdufresne]

• Add more ImageDraw.py tests and remove unused Draw.c code 2533
  [hugovk]

• Test: More tests for ImageMorph 2554
  [hugovk]

• Test: McIDAS area file 2552
  [radarhere]

• Update Feature Detection 2520
  [wiredfool]

• CI: Update pypy on TravisCI 2573
  [hugovk]

• ImageMorph: Fix wrong expected size of MRLs read from disk 2561
  [dov]

• Docs: Update install docs for FreeBSD 2546
  [wiredfool]

• Build: Ignore OpenJpeg 1.5 on FreeBSD 2544
  [melvyn-sopacua]

• Remove 'not yet implemented' methods from PIL 1.1.4 2538
  [hugovk]

• Dependencies: Update FreeType to 2.8, LibTIFF to 4.0.8 and libimagequant to 2.9.1 2535 2537 2540
  [radarhere]

• Raise TypeError and not also UnboundLocalError in ImageFile.Parser() 2525
  [joshblum]

• Test: Use Codecov for coverage 2528
  [hugovk]

• Use PNG for Image.show() 2527
  [HinTak, wiredfool]

• Remove WITH_DEBUG compilation flag 2522
  [wiredfool]

• Fix return value on parameter parse error in _webp.c 2521
  [adw1n]

• Set executable flag on scripts with shebang line 2295
  [radarhere]

• Flake8 2460
  [radarhere]

• Doc: Release Process Changes 2516
  [wiredfool]

• CI: Added region for s3 deployment on appveyor 2515
  [wiredfool]

• Doc: Updated references to point to existing files 2507
  [radarhere]

• Return copy on Image crop if crop dimensions match the image 2471
  [radarhere]

• Test: Optimize CI speed 2464, 2466
  [hugovk]

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖