Clearer spacing in index.md (#13733)

Perhaps this is just personal preference but I very rarely see the use of + without spaces on either side, it's a little jarring

files/en-us/learn/server-side/express_nodejs/displaying_data/bookinstance_detail_page_and_challenge/index.md

@@ -32,7 +32,7 @@ exports.bookinstance_detail = function(req, res, next) {
           return next(err);
         }
       // Successful, so render.
-      res.render('bookinstance_detail', { title: 'Copy: '+bookinstance.book.title, bookinstance:  bookinstance});
+      res.render('bookinstance_detail', { title: 'Copy: ' + bookinstance.book.title, bookinstance:  bookinstance});
     })
 
 };