minor #2515 Update internals.rst (pribilinskiy)

This PR was submitted for the 2.x branch but it was merged into the 1.x branch instead (closes #2515).

Discussion
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Update internals.rst

Missing an opening paren

Commits
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b8967bd3 Update internals.rst

doc/internals.rst

@@ -128,7 +128,7 @@ using)::
         {
             // line 1
             echo "Hello ";
-            echo twig_escape_filter($this->env, isset($context["name"]) ? $context["name"] : null), "html", null, true);
+            echo twig_escape_filter($this->env, (isset($context["name"]) ? $context["name"] : null), "html", null, true);
         }
 
         // some more code