Fix tests on Windows (#562)

* fix: replace `\` with `/` in git ref to fix `git_test.go` on windows

Paths on Windows use backslash (`\`) as directory separator and this breaks `TestGitFindRef()`.
Replacing `\` with `/` in git ref fixes that issue.

* fix: replace `gopkg.in/godo.v2/glob` with std library `path/filepath`

`github.com/go-godo/godo` lib has been last updated in 2016 and it also
depends on another outdated lib `github.com/MichaelTJones/walk` with
last update in 2016. This also fixes `permission_denied` errors on
Windows (and perhaps Linux in some specific cases). I'm not aware of
any performance improvement or drawback because of that change.

pkg/common/git.go

@@ -98,7 +98,8 @@ func findGitPrettyRef(head, root, sub string) (string, error) {
 		}
 		var pointsTo = strings.TrimSpace(string(bts))
 		if head == pointsTo {
-			name = strings.TrimPrefix(strings.Replace(path, root, "", 1), "/")
+			// On Windows paths are separated with backslash character so they should be replaced to provide proper git refs format
+			name = strings.TrimPrefix(strings.ReplaceAll(strings.Replace(path, root, "", 1), `\`, `/`), "/")
 			log.Debugf("HEAD matches %s", name)
 		}
 		return nil