Remove unnecessary RefCell, backport to Rust 1.36

src/input.rs

@@ -1,17 +1,16 @@
-use std::cell::RefCell;
 use std::fs;
 use std::io::{self, Read, Seek, SeekFrom};
 
 pub enum Input<'a> {
     File(fs::File),
-    Stdin(RefCell<io::StdinLock<'a>>),
+    Stdin(io::StdinLock<'a>),
 }
 
 impl<'a> Read for Input<'a> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         match *self {
             Input::File(ref mut file) => file.read(buf),
-            Input::Stdin(ref mut stdin) => stdin.borrow_mut().read(buf),
+            Input::Stdin(ref mut stdin) => stdin.read(buf),
         }
     }
 }
@@ -31,8 +30,8 @@ impl<'a> Seek for Input<'a> {
 impl<'a> Input<'a> {
     pub fn into_inner(self) -> Box<dyn Read + 'a> {
         match self {
-            Self::File(file) => Box::new(file),
-            Self::Stdin(stdin) => Box::new(stdin.into_inner()),
+            Input::File(file) => Box::new(file),
+            Input::Stdin(stdin) => Box::new(stdin),
         }
     }
 }