Merge commit 'a98e7ab8b9' into clippyup

src/tools/clippy/tests/ui/writeln_empty_string.fixed

@@ -8,13 +8,13 @@ fn main() {
     let mut v = Vec::new();
 
     // These should fail
-    writeln!(&mut v);
+    writeln!(v);
 
     let mut suggestion = Vec::new();
-    writeln!(&mut suggestion);
+    writeln!(suggestion);
 
     // These should be fine
-    writeln!(&mut v);
-    writeln!(&mut v, " ");
-    write!(&mut v, "");
+    writeln!(v);
+    writeln!(v, " ");
+    write!(v, "");
 }