Updated Pillow to 6.2 to fix DoS vulnerability

api/requirements/base.txt

@@ -5,7 +5,7 @@ django>=2.2.4,<2.3
 django-environ>=0.4,<0.5
 
 # Images
-Pillow>=5.4,<5.5
+Pillow>=6.2,<7
 
 # For user registration, either via email or social
 # Well-built with regular release cycles!