bump deps to make the package null safe

DetachHead · DetachHead · commit 2cd70c17f004 · 2022-07-10T21:47:45.000+10:00
diff --git a/pubspec.yaml b/pubspec.yaml
@@ -6,5 +6,5 @@ homepage: https://github.com/thosakwe/html_builder
 environment:
   sdk: ">=2.0.0-dev <3.0.0"
 dev_dependencies:
-  html: ^0.13.1
-  test: ^0.12.0
+  html: ^0.15.0
+  test: ^1.21.4
