Fix Linux policy platform (#46)

Author: ninxsoft

lib/linux-device-health.policies.yml

@@ -1,5 +1,5 @@
 - name: Linux - Enable disk encryption
-  platform: darwin
+  platform: linux
   description: This policy checks if disk encryption is enabled.
   resolution: As an IT admin, deploy an image that includes disk encryption.
   query: SELECT 1 FROM disk_encryption WHERE encrypted=1 AND name LIKE '/dev/dm-1';