Correct return type for onBeforeRequest and onAfterResponse (#610)

Author: hornta

lib/index.d.ts

@@ -40,8 +40,8 @@ interface UploadOptions {
   overridePatchMethod?: boolean
   headers?: { [key: string]: string }
   addRequestId?: boolean
-  onBeforeRequest?: (req: HttpRequest) => void
-  onAfterResponse?: (req: HttpRequest, res: HttpResponse) => void
+  onBeforeRequest?: (req: HttpRequest) => (void | Promise<void>)
+  onAfterResponse?: (req: HttpRequest, res: HttpResponse) => (void | Promise<void>)
 
   chunkSize?: number
   retryDelays?: number[]