docs: update 'networks.json' file

Bumped minimum Mithril signer version from '8.10.0-pre' to '8.11.0-pre'.

Author: jpraynaud

networks.json

@@ -114,7 +114,7 @@
   },
   "sanchonet": {
     "cardano-minimum-version": {
-      "mithril-signer": "8.10.0-pre"
+      "mithril-signer": "8.11.0-pre"
     },
     "mithril-networks": [
       {
@@ -142,4 +142,4 @@
       }
     ]
   }
-}
+}