Addons: docdiff compare against LATEST (#10820)

* Addons: docdiff compare against `default_branch`

Closes #154

* Addons: compare against LATEST -- `default_branch` is not correct

readthedocs/proxito/views/hosting.py

@@ -17,6 +17,7 @@
     ProjectSerializer,
     VersionSerializer,
 )
+from readthedocs.builds.constants import LATEST
 from readthedocs.builds.models import Version
 from readthedocs.core.resolver import resolver
 from readthedocs.core.unresolver import UnresolverError, unresolver
@@ -306,7 +307,9 @@ def _v0(self, project, version, build, filename, user):
                     # "http://test-builds-local.devthedocs.org/en/latest/index.html"
                     "base_url": resolver.resolve(
                         project=project,
-                        version_slug=project.get_default_version(),
+                        # NOTE: we are using LATEST version to compare against to for now.
+                        # Ideally, this should be configurable by the user.
+                        version_slug=LATEST,
                         language=project.language,
                         filename=filename,
                     )