flag: Fix up a package comment a bit.

I think "the flag" was a typo, and the word "after" was repetitive.

Change-Id: I81c034ca11a3a778ff1eb4b3af5b96bc525ab985
Reviewed-on: https://go-review.googlesource.com/10195Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

src/flag/flag.go

@@ -31,7 +31,7 @@
 		fmt.Println("ip has value ", *ip)
 		fmt.Println("flagvar has value ", flagvar)
 
-	After parsing, the arguments after the flag are available as the
+	After parsing, the arguments following the flags are available as the
 	slice flag.Args() or individually as flag.Arg(i).
 	The arguments are indexed from 0 through flag.NArg()-1.