updated to latest pxt

libs/core/shims.d.ts

@@ -950,6 +950,12 @@ declare interface Buffer {
     //% shim=BufferMethods::getUint8
     getUint8(off: int32): int32;
 
+    /**
+     * Returns false when the buffer can be written to.
+     */
+    //% shim=BufferMethods::isReadOnly
+    isReadOnly(): boolean;
+
     /**
      * Writes an unsigned byte at a particular location
      */