walletrpc: fix description of bumpfee.immediate

It waits for the next block and sends CPFP even if there are no other
inputs to form a batch.

lnrpc/walletrpc/walletkit.swagger.json

@@ -1440,7 +1440,7 @@
         },
         "immediate": {
           "type": "boolean",
-          "description": "Optional. Whether this input will be swept immediately. When set to true,\nthe sweeper will sweep this input without waiting for the next batch."
+          "description": "Optional. Whether this input will be swept immediately. When set to true,\nthe sweeper will sweep this input without waiting for the next block."
         },
         "budget": {
           "type": "string",