fix: install gentool with separated tag

[tr1v3r]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

fix #1125

according to https://golang.org/ref/mod#vcs-version

If a module is defined in a subdirectory within the repository, that is, the module subdirectory portion of the module path is not empty, then each tag name must be prefixed with the module subdirectory, followed by a slash. For example, the module golang.org/x/tools/gopls is defined in the gopls subdirectory of the repository with root path golang.org/x/tools. The version v0.4.0 of that module must have the tag named gopls/v0.4.0 in that repository.

User Case Description