delay cache eviction each time the metadata is requested

lib/commands/metadata.js

@@ -13,6 +13,7 @@ Data.getMetadataRaw = function (Env, channel /* channelName */, _cb) {
 
     var cached = Env.metadata_cache[channel];
     if (HK.isMetadataMessage(cached)) {
+        Env.checkCache(channel);
         return void cb(void 0, cached);
     }