Fix link capitalization in documentation of std::io::BufWriter.

Author: czipperz

src/libstd/io/buffered.rs

@@ -350,7 +350,7 @@ impl<R: Seek> Seek for BufReader<R> {
 ///
 /// It can be excessively inefficient to work directly with something that
 /// implements [`Write`]. For example, every call to
-/// [`write`][`Tcpstream::write`] on [`TcpStream`] results in a system call. A
+/// [`write`][`TcpStream::write`] on [`TcpStream`] results in a system call. A
 /// `BufWriter` keeps an in-memory buffer of data and writes it to an underlying
 /// writer in large, infrequent batches.
 ///
@@ -401,7 +401,7 @@ impl<R: Seek> Seek for BufReader<R> {
 /// the `stream` is dropped.
 ///
 /// [`Write`]: ../../std/io/trait.Write.html
-/// [`Tcpstream::write`]: ../../std/net/struct.TcpStream.html#method.write
+/// [`TcpStream::write`]: ../../std/net/struct.TcpStream.html#method.write
 /// [`TcpStream`]: ../../std/net/struct.TcpStream.html
 /// [`flush`]: #method.flush
 #[stable(feature = "rust1", since = "1.0.0")]