Add upper bound to dependency versions (#714)

* Add upper bound to dependency versions

This might save us from some troubles if a major release of one of those
dependency arrives (thinking of jupyter-client 7.0 coming)

* Update setup.py

Co-authored-by: David Brochart <david.brochart@gmail.com>

Co-authored-by: David Brochart <david.brochart@gmail.com>

setup.py

@@ -75,11 +75,11 @@ def run(self):
     python_requires='>=3.7',
     install_requires=[
         'importlib-metadata<4;python_version<"3.8.0"',
-        'debugpy>=1.0.0',
-        'ipython>=7.23.1',
-        'traitlets>=4.1.0',
-        'jupyter_client',
-        'tornado>=4.2',
+        'debugpy>=1.0.0,<2.0',
+        'ipython>=7.23.1,<8.0',
+        'traitlets>=4.1.0,<6.0',
+        'jupyter_client<7.0',
+        'tornado>=4.2,<7.0',
         'matplotlib-inline>=0.1.0,<0.2.0',
         'appnope;platform_system=="Darwin"',
     ],