Update minimum version of requests package (#492)

Author: Troy McConaghy

setup.py

@@ -12,7 +12,7 @@
     changelog = changelog_file.read()
 
 install_requires = [
-    'requests>=2.11.0',
+    'requests>=2.20.0',
     'cryptoconditions==0.8.0',
     'pysha3~=1.0.2',
     'python-rapidjson~=0.6.0',