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/cursor.rs

@@ -752,7 +752,8 @@ impl<'c, 'f> ir::InstInserterBase<'c> for &'c mut EncCursor<'f> {
         // Assign an encoding.
         // XXX Is there a way to describe this error to the user?
         #[cfg_attr(feature = "cargo-clippy", allow(match_wild_err_arm))]
-        match self.isa
+        match self
+            .isa
             .encode(&self.func, &self.func.dfg[inst], ctrl_typevar)
         {
             Ok(e) => self.func.encodings[inst] = e,