lru: fix misspelling  (#112)

diff --git a/lru/lru.go b/lru/lru.go
index 532cc45..eac1c76 100644
--- a/lru/lru.go
+++ b/lru/lru.go
@@ -25,7 +25,7 @@
 	// an item is evicted. Zero means no limit.
 	MaxEntries int
 
-	// OnEvicted optionally specificies a callback function to be
+	// OnEvicted optionally specifies a callback function to be
 	// executed when an entry is purged from the cache.
 	OnEvicted func(key Key, value interface{})