[Doc] Fixed the syntax of a table in messages.rst

doc/messages.rst

@@ -100,7 +100,7 @@ with a strict format, you only need to pass a DateTimeInterface instance to
 +-------------------------------+------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------+
 | ``Date``                      | Specifies the date at which the message was sent                                                                                   | ``getDate()`` / ``setDate()``               |
 +-------------------------------+------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------+
-| ``Content-Type``              | Specifies the format of the message (usually ``text/plain`` or ``text/html``)                                                              | ``getContentType()`` / ``setContentType()`` |
+| ``Content-Type``              | Specifies the format of the message (usually ``text/plain`` or ``text/html``)                                                      | ``getContentType()`` / ``setContentType()`` |
 +-------------------------------+------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------+
 | ``Content-Transfer-Encoding`` | Specifies the encoding scheme in the message                                                                                       | ``getEncoder()`` / ``setEncoder()``         |
 +-------------------------------+------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------+