Fix #510 : the interpolation is a placeholder

Author: Cerdic

src/Parser.php

@@ -2430,14 +2430,17 @@ protected function placeholder(&$placeholder)
     {
         if ($this->match(
             $this->utf8
-                ? '([\pL\w\-_]+|#[{][$][\pL\w\-_]+[}])'
-                : '([\w\-_]+|#[{][$][\w\-_]+[}])',
+                ? '([\pL\w\-_]+)'
+                : '([\w\-_]+)',
             $m
         )) {
             $placeholder = $m[1];
 
             return true;
         }
+        if ($this->interpolation($placeholder)) {
+            return true;
+        }
 
         return false;
     }