add Library "FlashStorage" for SAMD (M0 etc.) CPUs

.travis.yml

@@ -23,11 +23,11 @@ before_install:
     fi
   - arduino --pref "boardsmanager.additional.urls=" --save-prefs
 install:
-  - arduino --install-library "U8g2"
+  - arduino --install-library "U8g2","FlashStorage"
 script:
   - cp -f $PWD/crossbow/configurations/config_${CONFIG}.h $PWD/crossbow/config.h &&
     arduino --verify --board $BOARD $PWD/crossbow/crossbow.ino
 notifications:
   email:
     on_success: change
-    on_failure: change
+    on_failure: change