Test failure with recent PHPUnit version

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Discovered in Fedora QA since PHPUnit was updated to 6.4.3
https://apps.fedoraproject.org/koschei/package/php-zendframework-zend-mail?collection=f28

There were 4 failures:
1) ZendTest\Mail\Header\SenderTest::testFromStringWithInvalidInput with data set #0 ('Sender: foo', 'Zend\Mail\Exception\InvalidAr...eption')
Failed asserting that exception message is empty but is 'The input is not a valid email address. Use the basic format local-part@hostname'.
2) ZendTest\Mail\Header\SenderTest::testFromStringWithInvalidInput with data set #1 ('Sender: foo<foo>', 'Zend\Mail\Exception\InvalidAr...eption')
Failed asserting that exception message is empty but is 'The input is not a valid email address. Use the basic format local-part@hostname'.
3) ZendTest\Mail\Header\SenderTest::testFromStringWithInvalidInput with data set #2 ('Sender: foo foo', 'Zend\Mail\Header\Exception\In...eption')
Failed asserting that exception message is empty but is 'Invalid header value for Sender string'.
4) ZendTest\Mail\Header\SenderTest::testFromStringWithInvalidInput with data set #3 ('Sender: <foo> foo', 'Zend\Mail\Header\Exception\In...eption')
Failed asserting that exception message is empty but is 'Invalid header value for Sender string'.

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Also catched by travis on https://travis-ci.org/zendframework/zend-mail/jobs/289069386