rpmname: fix naming of goipaths with multi-character versions
    
    ```
    $ go2rpm --print-name github.com/AdamSLevy/jsonrpc2/v14
    golang-github-adamslevy-jsonrpc2_14
    $ rpm -E '%gorpmname -L github.com/AdamSLevy/jsonrpc2/v14'
    golang-github-adamslevy-jsonrpc2_14
    
    $ go2rpm --print-name --no-use-new-versioning github.com/AdamSLevy/jsonrpc2/v14
    golang-github-adamslevy-jsonrpc2-14
    $ rpm -E '%gorpmname github.com/AdamSLevy/jsonrpc2/v14'
    golang-github-adamslevy-jsonrpc2-14
    
    $ go2rpm --print-name  github.com/apparentlymart/go-textseg/v15
    golang-github-apparentlymart-textseg15
    ```
    
    Fixes: https://pagure.io/GoSIG/go2rpm/issue/34