Auto merge of #38648 - utkarshkukreti:question-mark-in-libstd-documentation-examples, r=pnkfelix,steveklabnik,frewsxcvx

libstd: replace all `try!` with `?` in documentation examples

See #38644.

For the record, I used the following Perl one-liner and then manually fixed a couple of things it got wrong:

    $ perl -p -i -e 's#(///.*)try!\((.*)\)#$1$2?#' src/libstd/**/*.rs

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/io/error.rs b/src/libstd/io/error.rs
index 434f522cc1e..6d4da2e6a88 100644
--- a/src/libstd/io/error.rs
+++ b/src/libstd/io/error.rs
@@ -39,7 +39,7 @@ use convert::From;
 /// fn get_string() -> io::Result<String> {
 ///     let mut buffer = String::new();
 ///
-///     try!(io::stdin().read_line(&mut buffer));
+///     io::stdin().read_line(&mut buffer)?;
 ///
 ///     Ok(buffer)
 /// }