Support Dexcom HIGH/LOW when device is share2

Using share2nightscout-bridge, the device property is defined as 'share2'

displayBg should honour the Dexcom HIGH and LOW values when the device is share2

This ensures that NightScout returns "LOW" for 39mg/dl and "HIGH" for 401mg/dl as is reported in the Dexcom app/receiver.

lib/sandbox.js

@@ -235,7 +235,7 @@ function init () {
   };
 
   sbx.displayBg = function displayBg (entry) {
-    var isDex = entry && (!entry.device || entry.device === 'dexcom');
+    var isDex = entry && (!entry.device || entry.device === 'dexcom' || entry.device === 'share2');
     if (isDex && Number(entry.mgdl) === 39) {
       return 'LOW';
     } else if (isDex && Number(entry.mgdl) === 401) {