Make requirements more flexible (#36)

Author: jbonzo

requirements.txt

@@ -1,19 +1,19 @@
-atomicwrites==1.3.0
-attrs==19.3.0
-certifi==2019.9.11
-chardet==3.0.4
-idna==2.8
-importlib-metadata==0.23
-more-itertools==7.2.0
-packaging==19.2
-pluggy==0.13.0
-py==1.8.0
-pyparsing==2.4.4
-pytest==5.2.2
-requests==2.22.0
-six==1.13.0
-urllib3==1.25.6
-wcwidth==0.1.7
-websocket-client==0.56.0
-websockets==8.0.2
-zipp==0.6.0
+atomicwrites>=1.3.0
+attrs>=19.3.0
+certifi>=2019.9.11
+chardet>=3.0.4
+idna>=2.8
+importlib-metadata>=0.23
+more-itertools>=7.2.0
+packaging>=19.2
+pluggy>=0.13.0
+py>=1.8.0
+pyparsing>=2.4.4
+pytest>=5.2.2
+requests>=2.22.0
+six>=1.13.0
+urllib3>=1.25.6
+wcwidth>=0.1.7
+websocket-client>=0.56.0
+websockets>=8.0.2
+zipp>=0.6.0