Update repositories.txt (#4909)

Add Naguissa's uHexLib library

Author: Naguissa

repositories.txt

@@ -4209,6 +4209,7 @@ https://github.com/Naguissa/uSevenSegmentLib
 https://github.com/Naguissa/uTimerLib
 https://github.com/Naguissa/uTimerBrokerLib
 https://github.com/Naguissa/uUnixDate
+https://github.com/Naguissa/uHexLib
 https://github.com/naiithink/musicians-mate
 https://github.com/nailujx86/ESP8266_multipart
 https://github.com/namino-cc/Namino_Library