Renamed https://github.com/dac1e/Dcf77Receiver to https://github.com/dac1e/DCF77RX

Renamed the repository, because it shall appear along with other repositories that all start with upper case letters DCF instead of DCF. Along with this change, the appendix Receiver was shortened to RX.

Author: dac1e

repositories.txt

@@ -7827,7 +7827,7 @@ https://github.com/4211421036/gsr-arduino
 https://github.com/4211421036/IoTModule
 https://github.com/Elrindel/SomfyReceiver
 https://github.com/thebestia90/AD5259
-https://github.com/dac1e/Dcf77Receiver
+https://github.com/dac1e/DCF77RX
 https://github.com/ImSpeddy/L298Nlib
 https://github.com/4211421036/githubiot
 https://github.com/christosneg/concurrentPID.git