Fix linter issues

packages/0x.js/src/contract_wrappers/token_registry_wrapper.ts

@@ -26,7 +26,7 @@ export class TokenRegistryWrapper extends ContractWrapper {
         const addresses = await this.getTokenAddressesAsync();
         const tokenPromises: Array<Promise<Token|undefined>> = _.map(
             addresses,
-            (address: string) => (this.getTokenIfExistsAsync(address)),
+            async (address: string) => this.getTokenIfExistsAsync(address),
         );
         const tokens = await Promise.all(tokenPromises);
         return tokens as Token[];

packages/0x.js/src/utils/exchange_transfer_simulator.ts

@@ -81,7 +81,7 @@ export class ExchangeTransferSimulator {
         this.store.setBalance(tokenAddress, userAddress, balance.minus(amountInBaseUnits));
     }
     private throwValidationError(failureReason: FailureReason, tradeSide: TradeSide,
-                                 transferType: TransferType): Promise<never> {
+                                 transferType: TransferType): never {
         const errMsg = ERR_MSG_MAPPING[failureReason][tradeSide][transferType];
         throw new Error(errMsg);
     }