Chore: Update to crate-docs 2.1.2

We need to limit sphinx-autobuild to a previous release. The new one has
raises build errors on our docs.

Author: amotl

docs/build.json

@@ -1,5 +1,5 @@
 {
   "schemaVersion": 1,
   "label": "docs build",
-  "message": "2.1.1"
+  "message": "2.1.2"
 }