Fix build

Author: schmidt-sebastian

scripts/emulator-testing/emulators/emulator.ts

@@ -40,7 +40,7 @@ export abstract class Emulator {
 
   download(): Promise<void> {
     return new Promise<void>((resolve, reject) => {
-      tmp.dir((err: Error, dir: string) => {
+      tmp.dir((err: Error|null, dir: string) => {
         if (err) reject(err);
 
         console.log(`Created temporary directory at [${dir}].`);