Added

• Added expose_retry_header and retry_header options for debugging purposes (thanks, @coudenysj)
• Travis CI now tests PHP v7.2

Changed

• Allow newer versions of PHPUnit in composer.json (match Guzzle composer.json PHPUnit requirements)

Fixed

• Refactored data provider method name in PHPUnit test (testRetryOccursWhenStatusCodeMatchesProvider → providerForRetryOccursWhenStatusCodeMatches)
• Use PHPUnit new namespaced class name
• Fix phpunit.xml.dist specification so that PHPUnit no longer emits warnings
• Travis CI should use lowest library versions on lowest supported version of PHP (v5.5, not 5.6)

Removed

• hhvm tests in Travis CI; they were causing builds to fail