Fix typo in IFeeEstimate (#557)

Author: Cryptok777

rpc/core/src/wasm/message.rs

@@ -1567,12 +1567,12 @@ declare! {
          * to sample enough "interesting" points on the feerate-to-time curve, so that the interpolation is meaningful.
          */
 
-        normalBucket : IFeerateBucket[];
+        normalBuckets : IFeerateBucket[];
         /**
         * An array of *low* priority feerate values. The first value of this vector is guaranteed to
         * exist and provide an estimation for sub-*hour* DAG inclusion.
         */
-        lowBucket : IFeerateBucket[];
+        lowBuckets : IFeerateBucket[];
     }
     "#,
 }