Fix dependencies

Author: renggli

pubspec.yaml

@@ -17,7 +17,7 @@ dependencies:
   petitparser: ^5.4.0
   xml: ^6.3.0
 dev_dependencies:
-  build_runner: ^2.4.0
+  build_runner: ^2.3.0
   build_web_compilers: ^3.2.0
   lints: ^2.0.0
   test: ^1.24.0