ebnf: update comment

(pointed out by jan.mercl@nic.cz)

R=iant, jan.mercl, rsc
CC=golang-dev
https://golang.org/cl/4515189

src/pkg/ebnf/ebnf.go

@@ -8,7 +8,7 @@
 //	Production  = name "=" [ Expression ] "." .
 //	Expression  = Alternative { "|" Alternative } .
 //	Alternative = Term { Term } .
-//	Term        = name | token [ "..." token ] | Group | Option | Repetition .
+//	Term        = name | token [ "…" token ] | Group | Option | Repetition .
 //	Group       = "(" Expression ")" .
 //	Option      = "[" Expression "]" .
 //	Repetition  = "{" Expression "}" .