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Fix typos in the documentation

Co-Authored-By: LukasKalbertodt <lukas.kalbertodt@gmail.com>

Author: tbu-

src/libstd/io/mod.rs

@@ -1340,11 +1340,11 @@ pub trait Seek {
     ///
     /// If you need to obtain the length of *many* streams and you don't care
     /// about the seek position afterwards, you can reduce the number of seek
-    /// operations by simply calling `seek(SeekFrom::End(0))` and use its
+    /// operations by simply calling `seek(SeekFrom::End(0))` and using its
     /// return value (it is also the stream length).
     ///
     /// Note that length of a stream can change over time (for example, when
-    /// data is appended to a file). So calling this method multiply times does
+    /// data is appended to a file). So calling this method multiple times does
     /// not necessarily return the same length each time.
     ///
     ///