Install latest mkdocs by default as we do with sphinx (#7869)

* Install latest mkdocs by default as we do with sphinx

* Use feature flag

Author: stsewd

readthedocs/doc_builder/python_environments.py

@@ -373,7 +373,11 @@ def install_core_requirements(self):
                 self.project.get_feature_value(
                     Feature.DEFAULT_TO_MKDOCS_0_17_3,
                     positive='mkdocs==0.17.3',
-                    negative='mkdocs<1.1',
+                    negative=self.project.get_feature_value(
+                        Feature.USE_MKDOCS_LATEST,
+                        positive='mkdocs<1.1',
+                        negative='mkdocs',
+                    ),
                 ),
             )
         else:

readthedocs/projects/models.py

@@ -1591,6 +1591,7 @@ def add_features(sender, **kwargs):
     USE_SPHINX_LATEST = 'use_sphinx_latest'
     DONT_INSTALL_DOCUTILS = 'dont_install_docutils'
     DEFAULT_TO_MKDOCS_0_17_3 = 'default_to_mkdocs_0_17_3'
+    USE_MKDOCS_LATEST = 'use_mkdocs_latest'
     USE_SPHINX_RTD_EXT_LATEST = 'rtd_sphinx_ext_latest'
     INSTALL_LATEST_SETUPTOOLS = 'install_latest_setuptoold'
 
@@ -1706,6 +1707,7 @@ def add_features(sender, **kwargs):
             DEFAULT_TO_MKDOCS_0_17_3,
             _('Install mkdocs 0.17.3 by default'),
         ),
+        (USE_MKDOCS_LATEST, _('Use latest version of MkDocs')),
         (
             USE_SPHINX_RTD_EXT_LATEST,
             _('Use latest version of the Read the Docs Sphinx extension'),