Upgrade Pillow to >=4.0

setup.py

@@ -27,7 +27,7 @@ install_requires = [
     "django-treebeard>=4.2.0,<5.0",
     "djangorestframework>=3.7.4,<4.0",
     "draftjs_exporter>=2.0,<2.1",
-    "Pillow>=2.6.1,<5.0",
+    "Pillow>=4.0.0,<6.0",
     "beautifulsoup4>=4.5.1,<5.0",
     "html5lib>=0.999,<1",
     "Unidecode>=0.04.14,<1.0",
@@ -41,7 +41,6 @@ testing_extras = [
     'mock>=1.0.0',
     'python-dateutil>=2.2',
     'pytz>=2014.7',
-    'Pillow>=2.7.0',
     'elasticsearch>=1.0.0,<3.0',
     'Jinja2>=2.8,<3.0',
     'boto3>=1.4,<1.5',