Remove duplicate 'extern crate'

src/output.rs

@@ -1,11 +1,11 @@
-extern crate shell_words;
-
 use std::env;
 use std::ffi::OsString;
 use std::io::{self, Write};
 use std::path::PathBuf;
 use std::process::{Child, Command, Stdio};
 
+use shell_words;
+
 use app::PagingMode;
 use errors::*;