words: mask more words in spellcheck

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

.words

@@ -1,7 +1,9 @@
 RPC
 RPCs
+blackholed
 cancelable
 cancelation
+cluster_proxy
 defragment
 defragmenting
 etcd
@@ -20,5 +22,8 @@ prefetching
 protobuf
 serializable
 teardown
+too_many_pings
 uncontended
 unprefixed
+unlisting
+