fold: fix clippy warnings

Author: phinjensen

src/uu/fold/src/fold.rs

@@ -155,7 +155,7 @@ fn fold_file_bytewise<T: Read>(mut file: BufReader<T>, spaces: bool, width: usiz
             break;
         }
 
-        if line.len() == 1 && *line.get(0).unwrap() == NL {
+        if line == [NL] {
             println!();
             line.truncate(0);
             continue;
@@ -186,7 +186,7 @@ fn fold_file_bytewise<T: Read>(mut file: BufReader<T>, spaces: bool, width: usiz
             // Don't duplicate trailing newlines: if the slice is "\n", the
             // previous iteration folded just before the end of the line and
             // has already printed this newline.
-            if slice == &[NL] {
+            if slice == [NL] {
                 break;
             }