Arduino_Code: fix include case - #1677

# The compilation fails
$ arduino-cli compile -b arduino:avr:uno Arduino_Code
In file included from /home/.../workspace/duino-coin/Arduino_Code/Arduino_Code.ino:33:0:
/home/.../workspace/duino-coin/Arduino_Code/duco_hash.h:3:10: fatal error: arduino.h: No such file or directory
 #include <arduino.h>
          ^~~~~~~~~~~
compilation terminated.


Used platform Version Path                                                     
arduino:avr   1.8.6   /home/.../.arduino15/packages/arduino/hardware/avr/1.8.6

# The file is actually Arduino.h, with a capital letter
$ find ~/.arduino15/packages/arduino/hardware/avr/1.8.6/cores -iname arduino.h  
/home/.../.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/Arduino.h

$ arduino-cli compile -b arduino:avr:uno Arduino_Code
Sketch uses 12812 bytes (39%) of program storage space. Maximum is 32256 bytes.
Global variables use 437 bytes (21%) of dynamic memory, leaving 1611 bytes for local variables. Maximum is 2048 bytes.

Used platform Version Path                                                     
arduino:avr   1.8.6   /home/.../.arduino15/packages/arduino/hardware/avr/1.8.6