update-license.go: add blank line after build tag

This silences "go install ./...". For some reason it started
complaining with go 1.4.2.

update-license.go

@@ -1,4 +1,5 @@
 // +build none
+
 /*
 This command generates GPL license headers on top of all source files.
 You can run it once per month, before cutting a release or just