groupcache.go: fix misspelling

groupcache.go

diff --git a/groupcache.go b/groupcache.go
index 316ca49..8cf714a 100644
--- a/groupcache.go
+++ b/groupcache.go
@@ -245,7 +245,7 @@
 		// be only one entry for this key.
 		//
 		// Consider the following serialized event ordering for two
-		// goroutines in which this callback gets called twice for hte
+		// goroutines in which this callback gets called twice for the
 		// same key:
 		// 1: Get("key")
 		// 2: Get("key")