Remove unnecessary lifetime param and simplify error handling

src/services/downloader/mod.rs

@@ -74,7 +74,7 @@ pub async fn download<'a>(
     Some((response, is_zip))
 }
 
-pub async fn download_chain<'a>(
+pub async fn download_chain(
     book: BookWithRemote,
     file_type: String,
     source_config: config::SourceConfig,

src/services/downloader/types.rs

@@ -20,7 +20,7 @@ pub struct DownloadResult {
 
 pub fn get_response_async_read(it: Response) -> impl AsyncRead {
     it.bytes_stream()
-        .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))
+        .map_err(std::io::Error::other)
         .into_async_read()
         .compat()
 }