fix error reporting in generator scripts

script/generate-tags.go

@@ -59,4 +59,8 @@ func main() {
 		rname[0] = unicode.ToUpper(rname[0])
 		printf("var %s = %s\n", string(rname), exp)
 	}
+
+	if err != nil {
+		log.Fatalln(err)
+	}
 }

script/promote-to-tags.go

@@ -51,4 +51,8 @@ func main() {
 	for _, si := range ss {
 		printf("var %s = html.%s\n", si, si)
 	}
+
+	if err != nil {
+		log.Fatalln(err)
+	}
 }