Fix version with leading v in rust client.

It does not cover all edge cases though so we may need to improve it over time.

Tested locally to confirm the fix. Will add a test later when revising the spec with more test cases.

Another way is to set the packageVersion directly via an option.

To fix #12271

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cc @frol (2017/07) @farcaller (2017/08) @richardwhiuk (2019/07) @paladinzh (2020/05)