rpc: pass current block target in rpc

This fixes the hash rate being wrong on testnet after the switch
to 2 minute blocks

src/rpc/core_rpc_server.cpp

@@ -119,6 +119,7 @@ namespace cryptonote
     res.height = m_core.get_current_blockchain_height();
     res.target_height = m_core.get_target_blockchain_height();
     res.difficulty = m_core.get_blockchain_storage().get_difficulty_for_next_block();
+    res.target = m_core.get_blockchain_storage().get_current_hard_fork_version() < 2 ? DIFFICULTY_TARGET_V1 : DIFFICULTY_TARGET;
     res.tx_count = m_core.get_blockchain_storage().get_total_transactions() - res.height; //without coinbase
     res.tx_pool_size = m_core.get_pool_transactions_count();
     res.alt_blocks_count = m_core.get_blockchain_storage().get_alternative_blocks_count();

src/rpc/core_rpc_server_commands_defs.h

@@ -273,6 +273,7 @@ namespace cryptonote
       uint64_t height;
       uint64_t target_height;
       uint64_t difficulty;
+      uint64_t target;
       uint64_t tx_count;
       uint64_t tx_pool_size;
       uint64_t alt_blocks_count;