Hide Back button when there is no history on first load.

res/app/docs/docs-controller.js

@@ -1,6 +1,13 @@
 module.exports =
   function DocsCtrl($rootScope, $scope, $window, $location) {
 
+    function hasHistory() {
+      // TODO: watch this
+      return $window.history.length > 1
+    }
+
+    $scope.hasHistory = hasHistory()
+
     $scope.goBack = function () {
       $window.history.back()
     }