Install fails on windows 10

[Klaboe]

The install script seems to identify windows by uname = MINGW. As of Win10 this has changed to MSYS_NT-10.0. This leads to the following output.

helm plugin install https://github.com/nouney/helm-gcs --debug

[debug] updating https://github.com/nouney/helm-gcs
[debug] symlinking C:\Users\Klaboe\.helm\cache\plugins\https-github.jparrowsec.cn-nouney-helm-gcs to C:\Users\Klaboe\.helm\plugins\helm-gcs
[debug] loading plugin from C:\Users\Klaboe\.helm\plugins\helm-gcs
[debug] running install hook: &{C:\Program Files\Git\usr\bin\sh.exe [sh -c cd $HELM_PLUGIN_DIR; ./scripts/install.sh] [] <nil> <nil> <nil> [] %!s(*syscall.SysProcAttr=<nil>) %!s(*os.Process=<nil>) <nil> <nil> <nil> %!s(bool=false) [] [] [] [] %!s(chan error=<nil>) %!s(chan struct {}=<nil>)} Installing helm-gcs 0.2.0 ...
tar.exe: Error opening archive: Failed to open 'helm-gcs_0.2.0_UNKNOWN:MSYS_NT-10.0_x86_64.tar.gz' helm-gcs 0.2.0 is correctly installed.

(...)

Installed plugin: gcs`

So it says that it is correctly installed, even though the un-tar'ing has failed for helm-gcs_0.2.0_UNKNOWN:MSYS_NT-10.0_x86_64.tar.gz.

So i propose 2 fixed:

1. include MSYS_NT-10.0 as a windows-identifyer, and
2. abort install if OS is unknown, as it seems unnecessary to try to un-tar an invalid file