fix typo

bigcache.go

@@ -155,7 +155,7 @@ func (c *BigCache) Set(key string, entry []byte) error {
 
 // Append appends entry under the key if key exists, otherwise
 // it will set the key (same behaviour as Set()). With Append() you can
-// concatenate multiple entries under the same key in an lock optimized way.
+// concatenate multiple entries under the same key in a lock optimized way.
 func (c *BigCache) Append(key string, entry []byte) error {
 	hashedKey := c.hash.Sum64(key)
 	shard := c.getShard(hashedKey)