build(deps-dev): update phpunit/phpunit requirement from ^6.0 to ^6.0 || ^7.0

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

Changelog

Sourced from phpunit/phpunit's changelog.

[7.5.18] - 2019-12-06

Fixed

• Fixed #3967: Cannot double interface that extends interface that extends \Throwable
• Fixed #3968: Test class run in a separate PHP process are passing when exit called inside

[7.5.17] - 2019-10-28

Fixed

• Fixed #3727: Problem hidden by PHPUnit's error handler
• Fixed #3863: \Countable needs to be checked before \EmptyIterator

[7.5.16] - 2019-09-14

Fixed

• Fixed #3801: Class constant as default parameter is undefined
• Fixed #3834: Trailing slash breaks code coverage on Windows

[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

... (truncated)

Commits

• fcf6c4b Prepare release
• 2902560 Update ChangeLog
• 773be5e Ignore .psalm directory on PHPUnit 7.5 branch
• afb88b4 Adding fix
• d9d7efa Updating the test with expected behaviour
• ca4411e Add test for running tests in child process which are calling "exit"
• 81b7b0e Closes #3967
• 6ef9ac8 Fix: Build for any push or pull request
• a1137f1 Update tools
• 677e1ae HTTP -> HTTPS
• Additional commits viewable in compare view

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[codecov-io]

Codecov Report

Merging #63 (ad76c5a) into master (8a71a9d) will decrease coverage by 0.48%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master      #63      +/-   ##
============================================
- Coverage     42.22%   41.73%   -0.49%     
+ Complexity      258      252       -6     
============================================
  Files            15       15              
  Lines           720      714       -6     
============================================
- Hits            304      298       -6     
  Misses          416      416              

Impacted Files	Coverage Δ	Complexity Δ
src/Generator/TwigGenerator.php	79.34% <0.00%> (-1.07%)	31.00% <0.00%> (-5.00%)
src/Util/Path.php	93.67% <0.00%> (-0.08%)	40.00% <0.00%> (-1.00%)
src/Console/BaseCommand.php	0.00% <0.00%> (ø)	32.00% <0.00%> (ø%)

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[dependabot-preview]

A newer version of phpunit/phpunit exists, but since this PR has been edited by someone other than Dependabot I haven't updated it. You'll get a PR for the updated version as normal once this PR is merged.