Update excerpter expectations for bug in dart format

Author: parlough

pkgs/excerpter/test_data/expected/plaster.md

@@ -42,4 +42,5 @@ void custom() {
 void template() {
   /* ... */
 }
+
 ```

pkgs/excerpter/test_data/expected/transforms.md

@@ -7,4 +7,5 @@
   void indent() {
     print('indent');
   }
+  
 ```