fix: correct helm binary in install script for environment that have both helm 2 and 3 installed

[astorath]

This fixes install-binary.sh to use correct helm binary

[deiga]

@astorath Can you describe what the problem is right now? Why is this fix needed?

[astorath]

@deiga Sure, the problems are, when you have helm binary named differently (helm2 or helm3 for instance):

1. Installation does not work sometimes (HELM_PLUGIN_DIR resolves to /plugins/helm-diff) because root fs might be readonly
2. /plugins/helm-diff is created polluting filesystem
3. The latest version is installed always (because git describe fails on empty /plugins/helm-diff)

PS: I also have a question about that. Would you be so kind to release special v2.11.0+6 tagged v2 release containing the same fix. I have github fork for that, but it would be nice to have the same issue fixed for helm2 in original repo.

[mumoshu]

Good catch! I've tried my best to rephrase the PR title to better capture the purpose of this fix. Thanks for your contribution @astorath ☺️

[mumoshu]

@deiga Thanks for your help on communication! I wouldn't have understood this without your conversation with @astorath