Add minimum Flask version requirement.

Install requires Flask version >= 1.0 for use of get_json method.

Author: smarlowucf

setup.py

@@ -30,7 +30,7 @@
       platforms='any',
       install_requires=[
           'Werkzeug>=0.14',  # Needed for SameSite cookie functionality
-          'Flask',
+          'Flask>=1.0',
           'PyJWT>=1.6.4',
           'six',
       ],