releasesjson: Fix missing Version in unmarshaled response

[radeksimko]

I cannot think of a good reason why we had the RawVersion field there. It may have pre-dated go-version's ability to unmarshal. Either way, this has led to a weird error message, as discovered by @bschaatsbergen in #191

 $ ./hc-install install -version 1.0.0 terraform
hc-install: will install terraform@1.0.0
failed to install terraform@1.0.0: no ZIP archive found for terraform <nil> darwin/arm64

After patch

$ go run ./cmd/hc-install install -version 1.0.0 terraform
hc-install: will install terraform@1.0.0
failed to install terraform@1.0.0: no ZIP archive found for terraform 1.0.0 darwin/arm64
exit status 1

[bschaatsbergen]

LGTM 🚀