Fixed #18: Not loading hammer.js when running on node.js

src/module/imports.js

@@ -5,4 +5,14 @@
 // Try to load dependencies from the global window object.
 // If not available there, load via require.
 var moment = (typeof window !== 'undefined') && window['moment'] || require('moment');
-var Hammer = (typeof window !== 'undefined') && window['Hammer'] || require('hammerjs');
+
+var Hammer;
+if (typeof window !== 'undefined') {
+  // load hammer.js only when running in a browser (where window is available)
+  Hammer = window['Hammer'] || require('hammerjs');
+}
+else {
+  Hammer = function () {
+    throw Error('hammer.js is only available in a browser, not in node.js.');
+  }
+}