Document y (years) time unit

lib/libvmod_std/vmod.vcc

@@ -113,7 +113,7 @@ $Function DURATION duration(STRING, DURATION)
 Description
 	Converts the string *s* to seconds. *s* must be quantified
 	with ms (milliseconds), s (seconds), m (minutes), h (hours),
-	d (days) or w (weeks) units. If *s* fails to parse,
+	d (days), w (weeks) or y (years) units. If *s* fails to parse,
 	*fallback* will be returned.
 Example
 	set beresp.ttl = std.duration("1w", 3600s);