KUBECONFIG environment variable doesn't get initialized correctly

[kailunshi]

First time using this provider so just wanted to thank you for starting on this.

First I got an error: Error: diffing release set: %!w(<nil>)
After setting the debug flag, the issue seems to be with helm not recognizing the KUBECONFIG env var.
2020-10-15T23:57:42.851Z [DEBUG] plugin.terraform-provider-helmfile_v0.9.0: Error: Failed to get release *** in namespace kube-system: exit status 1: Error: Kubernetes cluster unreachable: Get "http://localhost:8080/version?timeout=32s": dial tcp 127.0.0.1:8080: connect: connection refused

I dug deeper and found out the there is an extra line between "KUBECONFIG=" and the file name I specify in the env var list and as a result, helmfile and helm are not getting the right env var. the issue seems to be here: https://github.com/mumoshu/terraform-provider-helmfile/blob/master/pkg/helmfile/release_set.go#L186