GO_BUILD_MIRROR_URL is not working

[tkyggit]

1. mirror url is not expected checksum

https://github.com/go-nv/goenv/blob/40b645ae1b317a4395efa1a05dcc66b496c30ce2/plugins/go-build/bin/go-build#L512

maybe expected below

    local tarball_filename=$(basename $package_url)
    mirror_url="${GO_BUILD_MIRROR_URL}/$tarball_filename"

2. Is the variable IS_TEST in the http function under the wrong condition?

https://github.com/go-nv/goenv/blob/40b645ae1b317a4395efa1a05dcc66b496c30ce2/plugins/go-build/bin/go-build#L454

The URL of the mirror is passed in the url, but it is overwritten.