srpm/go.lua: fix handling of version numbers with multiple digits
    
    Fix handling of double digit version numbers, regression introduced in
    commit 65a2d82b029 ("srpm/go.lua: avoid remove char 'v' from project
    name").
    
    Example:
      $ grep goipath golang-github-playground-validator-10.spec
      %global goipath         github.com/go-playground/validator/v10
    
    Before this patch:
      $ rpmspec --srpm -q --qf '%{name}\n' golang-github-playground-validator-10.spec
      golang-github-playground-validator-v10
    
    After this patch:
      $ rpmspec --srpm -q --qf '%{name}\n' golang-github-playground-validator-10.spec
      golang-github-playground-validator-10