Shoehorn EXPERIMENTAL_I2CBUS into Travis test

.travis.yml

   - opt_enable ULTIMAKERCONTROLLER FILAMENT_LCD_DISPLAY
   - build_marlin
   #
-  # Enable BEZIER_CURVE_SUPPORT
+  # Enable BEZIER_CURVE_SUPPORT, EXPERIMENTAL_I2CBUS, and I2C_SLAVE_ADDRESS
   #
   - restore_configs
-  - opt_enable_adv BEZIER_CURVE_SUPPORT
+  - opt_enable_adv BEZIER_CURVE_SUPPORT EXPERIMENTAL_I2CBUS
+  - opt_set_adv I2C_SLAVE_ADDRESS 1
   - build_marlin
   #
   # Enable COREXY