Fix for STRONG_MODE_INVALID_CAST_FUNCTION_EXPR analyzer error with 1.22.0-dev.10.4 (#21)

diff --git a/lib/src/backends/chroot/chroot_file.dart b/lib/src/backends/chroot/chroot_file.dart
index 2e556e9..fe45325 100644
--- a/lib/src/backends/chroot/chroot_file.dart
+++ b/lib/src/backends/chroot/chroot_file.dart
@@ -40,7 +40,9 @@
         case FileSystemEntityType.NOT_FOUND:
           // Validation passed; delete the link to keep the delegate file
           // system's validation from getting in the way.
-          setUp = () async => await fileSystem.link(newPath).delete();
+          setUp = () async {
+            await fileSystem.link(newPath).delete();
+          };
           break;
         case FileSystemEntityType.DIRECTORY:
           throw new FileSystemException('Is a directory', newPath);
@@ -87,7 +89,9 @@
         case FileSystemEntityType.NOT_FOUND:
           // Validation passed; delete the link to keep the delegate file
           // system's validation from getting in the way.
-          setUp = () => fileSystem.link(newPath).deleteSync();
+          setUp = () {
+            fileSystem.link(newPath).deleteSync();
+          };
           break;
         case FileSystemEntityType.DIRECTORY:
           throw new FileSystemException('Is a directory', newPath);