dx self-update reported versions and git tags mismatch

dx self-update --list and other options report versions without prepending the `v` that is used for git tags and hence this fails:
```
$ dx self-update --version 0.7.0-rc.2
ERROR dx self-update: Failed to fetch release by tag
Caused by:
NetworkError: api request failed with status: 404 - for: "https://api.github.com/repos/dioxuslabs/dioxus/releases/tags/0.7.0-rc.2"
```
This works:
`dx self-update --version v0.7.0-rc.2`

dx self-update should either prepend the `v` or report the versions as expected by itself so using them doesn't result in errors.