time: fix comment about use of Location.cacheEnd

Fixes #14099.

Change-Id: I122e918bdc55fb185f4a4a797489b160219542d2
Reviewed-on: https://go-review.googlesource.com/18943
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/time/zoneinfo.go

@@ -21,7 +21,7 @@ type Location struct {
 	// To avoid the binary search through tx, keep a
 	// static one-element cache that gives the correct
 	// zone for the time when the Location was created.
-	// if cacheStart <= t <= cacheEnd,
+	// if cacheStart <= t < cacheEnd,
 	// lookup can return cacheZone.
 	// The units for cacheStart and cacheEnd are seconds
 	// since January 1, 1970 UTC, to match the argument