Bug fixes

Bug fixes

Fix main.go generation when executing on a windows machine (caddyserv…

…er#32)

* Fix main.go generation when executing on a windows machine

When normalizing the `importPath` it will try to write on `main.go` files with imports
like `github.com/caddyserver/xcaddy/c:\xcaddy`

* Apply CR suggestions

* Add test cases for sub-paths on normalizeImportPath

* Run windows tests only when GOOS matches