[BestPractices] fix alignment of YAML values

Author: xelaris

best_practices/templates.rst

@@ -153,7 +153,7 @@ name is irrelevant because you never use it in your own code):
         app.twig.app_extension:
             class:     AppBundle\Twig\AppExtension
             arguments: ["@markdown"]
-            public: false
+            public:    false
             tags:
                 - { name: twig.extension }