Pin pyjwt version (#1797)

* Pin pyjwt version

Pyjwt version is not fixed, which can cause syntax error for user since the release of breaking changes from pyjwt (https://pypi.org/project/PyJWT/#history)

* Update setup.py

Fixes #1796

requirements.txt

@@ -1,5 +1,5 @@
 requests>=2.14.0
-pyjwt
+pyjwt<2.0
 sphinx<3
 sphinx-rtd-theme<0.6
 Deprecated

setup.py

@@ -98,7 +98,7 @@ if __name__ == "__main__":
             "Topic :: Software Development",
         ],
         python_requires=">=3.6",
-        install_requires=["deprecated", "pyjwt", "requests>=2.14.0"],
+        install_requires=["deprecated", "pyjwt<2.0", "requests>=2.14.0"],
         extras_require={"integrations": ["cryptography"]},
         tests_require=["cryptography", "httpretty>=1.0.3"],
     )