Update README

Signed-off-by: Mohammad Kalim Akram <kalim.akram@jina.ai>

README.md

@@ -2766,7 +2766,7 @@ model-index:
   - dataset:
       config: default
       name: MTEB Cmnli (default)
-      revision: null
+      revision: None
       split: validation
       type: C-MTEB/CMNLI
     metrics: