Update to the rustfmt in rust 1.28, which is now stable.

Also, rustfmt's --write-mode=check is now named --check.

lib/codegen/src/verifier/flags.rs

@@ -98,7 +98,8 @@ impl<'a> FlagsVerifier<'a> {
                 }
 
                 // Does the instruction have an encoding that clobbers the CPU flags?
-                if self.encinfo
+                if self
+                    .encinfo
                     .as_ref()
                     .and_then(|ei| ei.operand_constraints(self.func.encodings[inst]))
                     .map_or(false, |c| c.clobbers_flags) && live_val.is_some()