fixing: WARNING: Explicit markup ends without a blank line;

admin_manual/configuration/configuration_preview.rst

@@ -69,6 +69,7 @@ There are two config options to set the maximum size of a preview.
     'preview_max_y' => null,
 
 .. code-block:: php
+
 By default, both config options are set to null. 'Null' is equal to no limit.
 Numeric values represent the size in pixel. The following code limits previews
 to a maximum size of 100px by 100px:
@@ -80,6 +81,7 @@ to a maximum size of 100px by 100px:
     'preview_max_y' => 100,
 
 .. code-block:: php
+
 'preview_max_x' represents the x-axis and 'preview_max_y' represents the y-axis.
 
 Maximum scale factor: