build: Snap versions should not have initial "v"

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3728

build.go

@@ -542,8 +542,12 @@ func buildSnap(target target) {
 	if snaparch == "armhf" {
 		goarch = "arm"
 	}
+	snapver := version
+	if strings.HasPrefix(snapver, "v") {
+		snapver = snapver[1:]
+	}
 	err = tmpl.Execute(f, map[string]string{
-		"Version": version,
+		"Version":      snapver,
 		"Architecture": snaparch})
 	if err != nil {
 		log.Fatal(err)