Install <2.2

Author: stsewd

readthedocs/doc_builder/python_environments.py

@@ -381,7 +381,11 @@ def install_core_requirements(self):
                     negative='sphinx<2',
                 ),
                 'sphinx-rtd-theme<0.5',
-                'readthedocs-sphinx-ext',
+                self.project.get_feature_value(
+                    Feature.USE_SPHINX_RTD_EXT_LATEST,
+                    positive='readthedocs-sphinx-ext',
+                    negative='readthedocs-sphinx-ext<2.2',
+                ),
             ])
 
         cmd = copy.copy(pip_install_cmd)