refactor(is_listening): rename the isListening function for consistency

Author: asas1asas200

src/rdm6300.cpp

@@ -123,7 +123,7 @@ void Rdm6300::listen(void)
 	_serial->listen();
 }
 
-bool Rdm6300::isListening(void)
+bool Rdm6300::is_listening(void)
 {
 	return _serial->isListening();
 }

src/rdm6300.h

@@ -41,7 +41,7 @@ class Rdm6300
 		uint32_t get_tag_id(void);
 		bool is_tag_near(void);
 		void listen(void);
-		bool isListening(void);
+		bool is_listening(void);
 	private:
 #ifdef RDM6300_HARDWARE_SERIAL
 		HardwareSerial *_hardware_serial = NULL;