add available mainnet seeds

add existing mainnet nodes as the seeder does not resolve initial addresses provided
https://github.com/miguelfreitas/twister-seeder/issues/7

main.cpp

@@ -423,7 +423,7 @@ extern "C" void* ThreadStats(void*) {
   } while(1);
 }
 
-static const string mainnet_seeds[] = {"seed.twister.net.co","seed2.twister.net.co","seed3.twister.net.co",""};
+static const string mainnet_seeds[] = {"seed.twister.net.co","seed2.twister.net.co","seed3.twister.net.co","twisterseed.tk","twisterarmyseed.tk",""};
 static const string testnet_seeds[] = {""};
 static const string *seeds = mainnet_seeds;