fixed eth_changed to be compatible with jsonrpc4.2

mix/Web3Server.cpp

@@ -55,7 +55,7 @@ void Web3Server::put(std::string const& _name, std::string const& _key, std::str
 	m_db[k] = _value;
 }
 
-Json::Value Web3Server::eth_changed(int const& _id)
+Json::Value Web3Server::eth_changed(int _id)
 {
 	return WebThreeStubServerBase::eth_changed(_id);
 }

mix/Web3Server.h

@@ -44,7 +44,7 @@ signals:
 	void newTransaction();
 
 protected:
-	virtual Json::Value eth_changed(int const& _id) override;
+	virtual Json::Value eth_changed(int _id) override;
 	virtual std::string eth_transact(Json::Value const& _json) override;
 	virtual std::string eth_call(Json::Value const& _json) override;