Health check should verify that it can talk to the toggle-store (aka DB).

This commit fixes #103 by doing a simple select against the features table.

lib/routes.js

@@ -1,7 +1,18 @@
+var knex = require('./dbPool');
+var logger = require('./logger');
+
 module.exports = function (app) {
 
     app.get('/health', function (req, res) {
-        res.json({health: 'GOOD'});
+        knex.select(1)
+            .from('features')
+            .then(function() {
+                res.json({health: 'GOOD'});
+            })
+            .catch(function(err) {
+                logger.error('Could not select from features, error was: ', err);
+                res.status(500).json({health: 'BAD'});
+            });
     });
 
-};
+};