Merge branch 'master' of github.com:awslabs/python-deequ into dev

Author: Calvin Wang

setup.py

@@ -22,9 +22,9 @@ def setup_package():
             "Programming Language :: Python :: 3",
             "License :: OSI Approved :: Apache Software License"
         ],
-        install_requires=['pyspark==2.4.7', 'pandas'],
+        install_requires=['pandas'],
         setup_requires=['pyspark==2.4.7', 'pytest-runner', 'pandas'],
-        tests_require=['pyspark==2.4.7','pytest', 'pandas']
+        tests_require=['pyspark==2.4.7', 'pytest', 'pandas']
 
     )