cache path issue on Windows

[itscaro]

v0.139.3

err: [release "pinpoint": fetching "git::https://github.com/pinpoint-apm/pinpoint-kubernetes.git@pinpoint?ref=master": get: error downloading 'https://github.com/pinpoint-apm/pinpoint-kubernetes.git?ref=master': CreateFile .helmfile\cache\pinpoint\git::https:\github.com\pinpoint-apm\pinpoint-kubernetes.git@pinpoint?ref=master\https_github_com_pinpoint-apm_pinpoint-kubernetes_git.ref=master: The filename, directory name, or volume label syntax is incorrect.; CreateFile .helmfile\cache\pinpoint\git::https:\github.com\pinpoint-apm\pinpoint-kubernetes.git@pinpoint?ref=master\https_github_com_pinpoint-apm_pinpoint-kubernetes_git.ref=master: The filename, directory name, or volume label syntax is incorrect.]
...
Path error in windows

Cache dir: .helmfile\cache\pinpoint\git::https:\github.com\pinpoint-apm\pinpoint-kubernetes.git@pinpoint?ref=master\https_github_com_pinpoint-apm_pinpoint-kubernetes_git.ref=master

Tried to sanitized chart URL with [^a-z0-9_-] => _

fatal: cannot write keep file 'E:/Data/workspace/github/helmfile/.test/.helmfile/cache/pinpoint/git__https___github_com_pinpoint-apm_pinpoint-kubernetes_git_pinpoint_ref_master/https_github_com_pinpoint-apm_pinpoint-kubernetes_git.ref=master/.git/objects/pack/pack-87115c11c9b9fd3824f439ab8ecb1ae9ba8a6d69.keep'
...
Path is too long on windows

Cache dir: .helmfile/cache/pinpoint/git__https___github_com_pinpoint-apm_pinpoint-kubernetes_git_pinpoint_ref_master/https_github_com_pinpoint-apm_pinpoint-kubernetes_git.ref=master

So I tried to remove the r.Chart in the path, maybe it's redundant?
PR will give this cache dir: .helmfile/cache/pinpoint/https_github_com_pinpoint-apm_pinpoint-kubernetes_git.ref=master

[mumoshu]

LGTM. Thanks a lot for finding and fixing this @itscaro ☺️