[ci skip] bump docs version

Author: Bulat Shakirzyanov

docs.yaml

@@ -30,7 +30,7 @@ links:
     href:  https://github.com/datastax/ruby-driver/releases
 versions:
   - name: v2.1.3
-    ref:  c93eac55227e1d188d863d53bf5a90df95264dba
+    ref:  df155c3093537a5ed6cb6db1322ce2873ddaaed4
   - name: v2.0.1
     ref:  80cab0ad188511ec16eb39111c0b67329c754729
   - name: v1.2.0