Add node version to debug log

The chrome, electron, and signal versions are already included in the
user agent string.

// FREEBIE

js/debugLog.js

@@ -57,7 +57,7 @@
         };
         console.get = function() {
             return window.navigator.userAgent +
-                ' Signal-Desktop/' + window.config.version +
+                ' node/' + window.config.node_version +
                 '\n' + log.print();
         };
         console.post = function(log) {

main.js

@@ -95,7 +95,8 @@ function createWindow () {
       version: package_json.version,
       buildExpiration: config.get('buildExpiration'),
       serverUrl: config.get('serverUrl'),
-      environment: environment
+      environment: environment,
+      node_version: process.versions.node
     }
   }))