narrow requests version bounds (#538)

Author: jesterhazy

setup.py

@@ -35,7 +35,7 @@ def read(fname):
 # Declare minimal set for installation
 required_packages = ['boto3>=1.9.55', 'numpy>=1.9.0', 'protobuf>=3.1', 'scipy>=0.19.0',
                      'urllib3>=1.21', 'PyYAML>=3.2, <4', 'protobuf3-to-dict>=0.1.5',
-                     'docker-compose>=1.23.0', 'requests>=2.14.2, !=2.18.0, <2.21']
+                     'docker-compose>=1.23.0', 'requests>=2.20.0, <2.21']
 
 # enum is introduced in Python 3.4. Installing enum back port
 if sys.version_info < (3, 4):