transpile: tests: specify --edition 2021 for rustfmt, too

Author: kkysen

c2rust-transpile/tests/snapshots.rs

@@ -88,7 +88,12 @@ fn transpile(platform: Option<&str>, c_path: &Path) {
         }
     };
 
-    let status = Command::new("rustfmt").arg(&rs_path).status();
+    let edition = "2021";
+
+    let status = Command::new("rustfmt")
+        .args(["--edition", edition])
+        .arg(&rs_path)
+        .status();
     assert!(status.unwrap().success());
 
     let rs = fs::read_to_string(&rs_path).unwrap();
@@ -119,7 +124,7 @@ fn transpile(platform: Option<&str>, c_path: &Path) {
             "--crate-type",
             "lib",
             "--edition",
-            "2021",
+            edition,
             "--crate-name",
             crate_name,
             "-o",