tinylab_test_code: Fix compilation with recent Arduino libraries

[gmacario]

Tested with Arduino 1.8.2 (Windows 10) and the following libraries loaded by the Arduino Library Manager:

• DS1307RTC Version 1.4.0
• LedControl Version 1.0.6
• LiquidTWI2-master Version unknown (from https://github.com/lincomatic/LiquidTWI2)
• RF24 Version 1.3.0
• RotaryEncoder Version 1.1.0
• SdFat Version 1.0.3
• Time Version 1.5.0
• extEEPROM Version 3.3.5

Fix https://github.com/sixfab/tinylab/issues/6

Signed-off-by: Gianpaolo Macario gmacario@gmail.com