helm-diff: Helm diff plugin doesn't work with dependencies charts

Hello everybody,

First of all, thanks for the work 👏💪

I have a chart which use an other chart as a dependency. When I override values for the dependency chart, the diff doesn’t output any changes incoming, which is different from the upgrade command which applies well the changes.

Does the dependencies are handled by this awesome plugin?

To help the investigations, I created a simple repository to show the structure: https://github.com/firehist/helm-diff-dependencies

Here are versions:

➜ helm3 version
version.BuildInfo{Version:"v3.5.0", GitCommit:"32c22239423b3b4ba6706d450bd044baffdcf9e6", GitTreeState:"clean", GoVersion:"go1.15.6"

➜ kubectl version
Client Version: version.Info{Major:"1", Minor:"16", GitVersion:"v1.16.0", GitCommit:"2bd9643cee5b3b3a5ecbd3af49d09018f0773c77", GitTreeState:"clean", BuildDate:"2019-09-18T14:36:53Z", GoVersion:"go1.12.9", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"18+", GitVersion:"v1.18.20-gke.501", GitCommit:"de876a981b936ce528482c45794fb1dfc5005042", GitTreeState:"clean", BuildDate:"2021-06-25T02:54:31Z", GoVersion:"go1.13.15b4", Compiler:"gc", Platform:"linux/amd64"}

helm-diff-dependencies on  main
➜ helm3 plugin list
NAME       	VERSION   	DESCRIPTION
2to3       	0.8.0     	migrate and cleanup Helm v2 configuration and releases in-place to Helm v3
diff       	3.1.3     	Preview helm upgrade changes as a diff
mapkubeapis	0.0.15    	Map release deprecated Kubernetes APIs in-place

Thanks a lot.