Change the server_error code to 500

Modify the corresponding test to accept error code 500

Author: MartinLoeper

lib/errors/server-error.js

@@ -18,7 +18,7 @@ var util = require('util');
 
 function ServerError(message, properties) {
   properties = _.assign({
-    code: 503,
+    code: 500,
     name: 'server_error'
   }, properties);
 

test/integration/handlers/token-handler_test.js

@@ -293,7 +293,7 @@ describe('TokenHandler integration', function() {
         .then(should.fail)
         .catch(function() {
           response.body.should.eql({ error: 'server_error', error_description: 'Unhandled exception' });
-          response.status.should.equal(503);
+          response.status.should.equal(500);
         });
     });