Update Arduino core to v3.1.2

Author: valeros

platform.json

@@ -49,7 +49,7 @@
       "type": "framework",
       "optional": true,
       "owner": "platformio",
-      "version": "~3.30101.0"
+      "version": "~3.30102.0"
     },
     "framework-esp8266-rtos-sdk": {
       "type": "framework",