setup.py: limit responses version for moto (iterative#4879)

```
c:\hostedtoolcache\windows\python\3.6.8\x64\lib\site-packages\moto\core\models.py:17: in <module>
    import responses
c:\hostedtoolcache\windows\python\3.6.8\x64\lib\site-packages\responses.py:29: in <module>
    from urllib3.connection import HTTPHeaderDict
E   ImportError: cannot import name 'HTTPHeaderDict'
```

setup.py

@@ -131,10 +131,13 @@ def run(self):
     "pydocstyle<4.0",
     "jaraco.windows==3.9.2",
     "mock-ssh-server>=0.8.2",
-    "moto==1.3.14.dev464",
+    "moto==1.3.16.dev110",
     # moto's indirect dependency that is causing problems with flufl.lock's
     # dependency (atpublic). See https://github.com/iterative/dvc/pull/4853
     "aws-sam-translator<1.29.0",
+    # for moto's indirect dependency.
+    # See https://github.com/iterative/dvc/pull/4879
+    "urllib3<1.26.0",
     "rangehttpserver==1.2.0",
     "beautifulsoup4==4.4.0",
     "flake8-bugbear",