Update Arduino-mbed core to v4.2.4

Author: valeros

platform.json

@@ -66,7 +66,7 @@
       "type": "framework",
       "optional": true,
       "owner": "platformio",
-      "version": "~4.2.1"
+      "version": "~4.2.4"
     },
     "framework-cmsis": {
       "type": "framework",