USize -> U32 (#839)

- Possibly a fix for https://github.com/polkadot-js/api/issues/838

packages/types/src/primitive/USize.ts

@@ -2,13 +2,13 @@
 // This software may be modified and distributed under the terms
 // of the Apache-2.0 license. See the LICENSE file for details.
 
-import U64 from './U64';
+import U32 from './U32';
 
 /**
  * @name USize
  * @description
  * A System default unsigned number, typically used in RPC to report non-consensus
- * data. It is a wrapper for [[U64]] as a 64-binary default
+ * data. It is a wrapper for [[U32]] as a WASM default (as generated by Rust bindings)
  */
-export default class USize extends U64 {
+export default class USize extends U32 {
 }