docs(versions): remove the trailing slash in URLs when switch versions

Because `https://docs.angularjs.org/api/` can handler the trailing slash,
but `https://code.angularjs.org/1.2.24/docs/api` can not.

Fix angular#9043
Closes angular#9045

Author: bolasblack

docs/app/src/versions.js

@@ -19,7 +19,7 @@ angular.module('versions', [])
   };
 
   $scope.jumpToDocsVersion = function(version) {
-    var currentPagePath = $location.path();
+    var currentPagePath = $location.path().replace(/\/$/, '');
 
     // TODO: We need to do some munging of the path for different versions of the API...