Fix compilation errors for lower versions (2.x) #11

Job	Run time
build (examples/UnitTestExample/UnitTestExample.ino)	51s
build (examples/ETHOTA/ETHOTA.ino)	54s
build (examples/HelloServer/HelloServer.ino)	59s
build (examples/SDWebServer/SDWebServer.ino)	1m 1s
build (examples/MQTTClient/MQTTClient.ino)	48s
build (examples/ESPMQTTSClient/ESPMQTTSClient.ino)	46s
build (examples/StaticIPAddress/StaticIPAddress.ino)	47s
build (examples/UDPClientReceiver/UDPClientReceiver.ino)	56s
build (examples/UDPClientSender/UDPClientSender.ino)	58s
build (examples/UDPClientReceiverDirectPC/UDPClientReceiverDirectPC.ino)	50s
build (examples/UDPClientSenderDirectPC/UDPClientSenderDirectPC.ino)	55s
build (examples/AsyncUDPServer/AsyncUDPServer.ino)	52s
build (examples/AsyncUDPClient/AsyncUDPClient.ino)	55s
build (examples/WebSocketClient/WebSocketClient.ino)	52s
build (examples/WebSocketServer/WebSocketServer.ino)	50s
build (examples/TCPClient/TCPClient.ino)	54s
build (examples/TCPServer/TCPServer.ino)	47s
build (examples/InternetComTest/InternetComTest.ino)	1m 0s
	15m 55s

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