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/regalloc/context.rs

@@ -140,13 +140,8 @@ impl Context {
         }
 
         // Pass: Coloring.
-        self.coloring.run(
-            isa,
-            func,
-            domtree,
-            &mut self.liveness,
-            &mut self.tracker,
-        );
+        self.coloring
+            .run(isa, func, domtree, &mut self.liveness, &mut self.tracker);
 
         if isa.flags().enable_verifier() {
             verify_context(func, cfg, domtree, isa)?;