Update repositories.txt (#5110)

Arduino library for 18 bit ADC I2C MCP3424 and compatibles.

Author: RobTillaart

repositories.txt

@@ -5300,6 +5300,7 @@ https://github.com/RobTillaart/MCP23008
 https://github.com/RobTillaart/MCP23017_RT
 https://github.com/RobTillaart/MCP23S08
 https://github.com/RobTillaart/MCP23S17
+https://github.com/RobTillaart/MCP3424
 https://github.com/RobTillaart/MCP4261
 https://github.com/RobTillaart/MCP4725
 https://github.com/RobTillaart/MCP9808_RT