Update phpunit/phpunit requirement from ^7.1 to ^7.5

[dependabot-preview]

Updates the requirements on phpunit/phpunit to permit the latest version.

Changelog

Sourced from phpunit/phpunit's changelog.

[7.5.15] - 2019-08-21

Changed

• Implemented #3765: Use ReflectionType::getName() instead of ReflectionType::__toString() (which is deprecated in PHP 7.4)

[7.5.14] - 2019-07-15

Fixed

• Fixed #3743: EmptyIterator instances are not handled correctly by Count and IsEmpty constraints

[7.5.13] - 2019-06-19

Fixed

• Fixed #3722: getObjectForTrait() does not work for traits that declare a constructor
• Fixed #3723: Unescaped dash in character group in regular expression

[7.5.12] - 2019-05-28

Changed

• After each test, libxml_clear_errors() is now called to clear the libxml error buffer

Fixed

• Fixed #3694: Constructor arguments for Throwable and Exception are ignored
• Fixed #3709: Method-level @coversNothing annotation does not prevent code coverage data collection

[7.5.11] - 2019-05-14

Fixed

• Fixed #3683: Regression in PHPUnit 7.5.10 with regard to Exception stubbing/mocking

[7.5.10] - 2019-05-09

Fixed

• Fixed #3414: willThrowException() only accepts Exception, not Throwable
• Fixed #3587: .phpunit.result.cache file is all over the place
• Fixed #3596: Mocking an interface that extends another interface forgets to mock its own methods
• Fixed #3674: TypeError when an incorrect file path is given

[7.5.9] - 2019-04-19

Fixed

• Fixed #3607: Return value generation interferes with proxying to original method

... (truncated)

Commits

• d79c053 Prepare release
• 062dfa4 Reorder
• c3e529e Do not run php-cs-fixer on build/
• 2cfde30 Update tools
• e11397f Move ReflectionType::__toString() cases to getName()
• 2834789 Prepare release
• 7cf0771 Add missing default value
• e2e8fb6 Remove empty space that GH editor added
• 4c7d5f6 Add test for prefix of just '0'
• c2e938d Fix phpcs error
• Additional commits viewable in compare view

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