Bump pillow from 4.2.1 to 6.2.0 in /requirements

Bumps [pillow](https://github.com/python-pillow/Pillow) from 4.2.1 to 6.2.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@4.2.1...6.2.0)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements/base.txt

@@ -14,7 +14,7 @@ gunicorn==19.7.1
 ipdb==0.10.3
 ipython==6.1.0
 markdown
-Pillow==4.2.1
+Pillow==6.2.0
 pip-tools==3.1.0
 psycopg2==2.7.3.1
 pytz==2017.2

requirements/local_compiled.txt

@@ -53,7 +53,7 @@ paramiko==2.3.1           # via fabric, fabric3
 parso==0.1.0              # via jedi
 pexpect==4.2.1            # via ipython
 pickleshare==0.7.4        # via ipython
-pillow==4.2.1
+pillow==6.2.0
 pip-tools==3.1.0
 prompt-toolkit==1.0.15    # via ipython
 psycopg2==2.7.3.1

requirements/production_compiled.txt

@@ -38,7 +38,7 @@ paramiko==2.3.1           # via fabric3
 parso==0.1.0              # via jedi
 pexpect==4.3.0            # via ipython
 pickleshare==0.7.4        # via ipython
-pillow==4.2.1
+pillow==6.2.0
 pip-tools==3.1.0
 prompt-toolkit==1.0.15    # via ipython
 psycopg2==2.7.3.1