fix #644 (#645)

Nice.  Good catch.

Author: barrowsys

src/web/clients/download/basic.md

@@ -6,12 +6,12 @@ Creates a temporary directory with [`tempfile::Builder`] and downloads
 a file over HTTP using [`reqwest::get`] asynchronously.
 
 Creates a target [`File`] with name obtained from [`Response::url`] within
-[`tempdir()`] and copies downloaded data into it with [`io::copy`].
+[`tempdir()`] and writes downloaded data into it with [`Writer::write_all`].
 The temporary directory is automatically removed on program exit.
 
 ```rust,edition2018,no_run
 use error_chain::error_chain;
-use std::io::copy;
+use std::io::Write;
 use std::fs::File;
 use tempfile::Builder;
 
@@ -41,15 +41,15 @@ async fn main() -> Result<()> {
         println!("will be located under: '{:?}'", fname);
         File::create(fname)?
     };
-    let content =  response.text().await?;
-    copy(&mut content.as_bytes(), &mut dest)?;
+    let content =  response.bytes().await?;
+    dest.write_all(&content)?;
     Ok(())
 }
 ```
 
 [`File`]: https://doc.rust-lang.org/std/fs/struct.File.html
-[`io::copy`]: https://doc.rust-lang.org/std/io/fn.copy.html
 [`reqwest::get`]: https://docs.rs/reqwest/*/reqwest/fn.get.html
 [`Response::url`]: https://docs.rs/reqwest/*/reqwest/struct.Response.html#method.url
 [`tempfile::Builder`]: https://docs.rs/tempfile/*/tempfile/struct.Builder.html
-[`tempdir()`]: https://docs.rs/tempfile/3.1.0/tempfile/struct.Builder.html#method.tempdir
+[`tempdir()`]: https://docs.rs/tempfile/*/tempfile/struct.Builder.html#method.tempdir
+[`Writer::write_all`]: https://doc.rust-lang.org/std/io/trait.Write.html#method.write_all