Bump phpunit/phpunit from 4.8.27 to 4.8.28

[dependabot[bot]]

Bumps phpunit/phpunit from 4.8.27 to 4.8.28.

Changelog

Sourced from phpunit/phpunit's changelog.

[4.8.28] - 2016-11-14

Fixed

• Improved the fix for #1955: Process isolation fails when running tests with phpdbg -qrr

Commits

• 558a3a0 Prepare release
• 03bf7e0 Update ChangeLog
• 284a69f Correct fix for #1956
• 7b58ff0 Revert "Closes #2300"
• d99e588 Closes #2300
• a270f42 Cleanup
• 41433b0 Composer does not work in Travis CI's PHP 5.3.3 environment
• 186ade5 Revert "Use Composer from build/tools/composer"
• dcc3675 Use Composer from build/tools/composer
• ca41092 Remove gitter.im hook
• Additional commits viewable in compare view

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