bug: update downloads original install version

[bassco]

The issue

The installer script uses the same logic for install or update and therefore installs the original version upon update.

https://github.com/databus23/helm-diff/blob/master/install-binary.sh#L71

How I tested:

helm plugin install https://github.com/databus23/helm-diff --version v3.1.1
helm plugin list |grep -E "NAME|^diff"
NAME            	VERSION	DESCRIPTION
diff            	3.1.1  	Preview helm upgrade changes as a diff

helm plugin update diff
Downloading https://github.com/databus23/helm-diff/releases/download/v3.1.1/helm-diff-macos.tgz
.....

What I was expecting:

helm plugin update diff
Downloading https://github.com/databus23/helm-diff/releases/download/v3.1.3/helm-diff-macos.tgz
.....

Some testing:

helm version --client --short
v3.2.4+g0ad800e
cd ~/Library/helm/plugins/helm-diff
git describe --tags --exact-match
v3.1.1
git rev-parse HEAD
5018bd7cd7312c5a33f75dfa9748cba7b0d5dc6f
git fetch --tags
git rev-parse HEAD
5018bd7cd7312c5a33f75dfa9748cba7b0d5dc6f
git describe --tags --exact-match
v3.1.1
git describe --tags `git rev-list --tags --max-count=1`
v3.1.3
git checkout v3.1.3
helm plugin update diff
Downloading https://github.com/databus23/helm-diff/releases/download/v3.1.3/helm-diff-macos.tgz

Root cause:

https://github.com/databus23/helm-diff/blob/master/plugin.yaml#L11

The installer script needs to known which mode it is running in.

hooks:
  install: "$HELM_PLUGIN_DIR/install-binary.sh"
  update: "$HELM_PLUGIN_DIR/install-binary.sh"

• install mode; use the current vcs tag
• update mode; get the latest remote tag

This can be achieved by prefixing the update command with an ENV var or passing a parameter, the common installer script can differentiate which mode it is in.

[bassco]

@databus23 are you able to review this change?

[mumoshu]

#309 has been merged! Thanks for your contribution @bassco ☺️