[gym/common] gym>=0.22.0 is not supported because of GoalEnv removal …

…and drop of Python 3.6.

python/gym_jiminy/common/setup.py

@@ -63,7 +63,7 @@
         # - 0.18.0: dtype handling of flatten space
         # - >=0.18.0,<0.18.3 requires Pillow<8.0 to work, not compatible with
         #   Python 3.9.
-        "gym>=0.18.3"
+        "gym>=0.18.3,<0.22.0"
     ],
     extras_require=extras,
     zip_safe=False