Update sendSmartTransaction's lastValidBlockHeightOffset type definit…

…ion (#132)

lastValidBlockHeightOffset is meant to default to 150, and should not be required by the consumer to specify. So I'm simply updating the type here to be an optional parameter because if we don't the change would be seemingly non-backwards-compatible (users can just specify lastValidBlockHeightOffset of 150 though) and would require a major version change otherwise

src/RpcClient.ts

@@ -712,7 +712,7 @@ export class RpcClient {
     lookupTables: AddressLookupTableAccount[] = [],
     sendOptions: SendOptions & {
       feePayer?: Signer;
-      lastValidBlockHeightOffset: number;
+      lastValidBlockHeightOffset?: number;
     } = { skipPreflight: false, lastValidBlockHeightOffset: 150 }
   ): Promise<TransactionSignature> {
     if (sendOptions.lastValidBlockHeightOffset < 0)