flutter package template is missing an assets section in pubspec.yaml

https://github.com/flutter/flutter/blob/master/packages/flutter_tools/templates/package/pubspec.yaml.tmpl

should have something similar to the app template:

https://github.com/flutter/flutter/blob/master/packages/flutter_tools/templates/create/pubspec.yaml.tmpl
