integrate into CI the minimal spiffs partition scheme

.travis.yml

@@ -5,7 +5,7 @@ env:
   - BD=arduino:avr:mega:cpu=atmega2560
   - BD=esp8266:esp8266:nodemcuv2:CpuFrequency=80,FlashSize=4M3M
   - BD=esp8266:esp8266:d1_mini:CpuFrequency=80,FlashSize=4M3M
-  - BD=espressif:esp32:esp32doit-devkit-v1:FlashFreq=80
+  - BD=espressif:esp32:esp32:PartitionScheme=min_spiffs,FlashFreq=80
 before_install:
   - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_1.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :1 -ac -screen 0 1280x1024x16"
   - sleep 3