Update to rustfmt-preview (#348)

* Update to rustfmt-preview.

* Run "cargo fmt --all" with rustfmt 0.4.1.

rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.

* Fix a long line that rustfmt 0.4.1 can't handle.

* Remove unneeded commas left behind by rustfmt.

lib/codegen/src/iterators.rs

@@ -87,8 +87,7 @@ mod tests {
             vec![]
         );
         assert_eq!(
-            []
-                .iter()
+            [].iter()
                 .cloned()
                 .adjacent_pairs()
                 .collect::<Vec<(i32, i32)>>(),