Remove PHP 5.4 from travis builds

[tPl0ch]

PHP 5.4 has reached end of life I don't understand why the travis run for PHP 5.4 is still required. See https://travis-ci.org/doctrine/doctrine2/jobs/135986241

It currently breaks travis builds for new PRs, i.e. the UnitOfWorkTest is using the Country::class notation which was introduced in PHP 5.5 (which will actually reach EOL very soon, too).

Not sure if making UnitOfWorkTest use get_class() for now, or just remove PHP 5.4 from the travis build.

$ php -v
PHP 5.4.40-1~dotdeb+wheezy.1 (cli) (built: Apr 22 2015 06:50:56) 
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2014 Zend Technologies
    with Xdebug v2.3.2, Copyright (c) 2002-2015, by Derick Rethans
    with Zend OPcache v7.0.3-dev, Copyright (c) 1999-2013, by Zend Technologies
$ ./vendor/bin/phpunit tests/Doctrine/Tests/ORM/UnitOfWorkTest.php 
PHP Parse error:  syntax error, unexpected 'class' (T_CLASS), expecting identifier (T_STRING) or variable (T_VARIABLE) or '{' or '$' in /vagrant/libs/doctrine2/tests/Doctrine/Tests/ORM/UnitOfWorkTest.php on line 343
PHP Stack trace:
PHP   1. {main}() /vagrant/libs/doctrine2/vendor/phpunit/phpunit/phpunit:0
PHP   2. PHPUnit_TextUI_Command::main() /vagrant/libs/doctrine2/vendor/phpunit/phpunit/phpunit:47
PHP   3. PHPUnit_TextUI_Command->run() /vagrant/libs/doctrine2/vendor/phpunit/phpunit/src/TextUI/Command.php:100
PHP   4. PHPUnit_Runner_BaseTestRunner->getTest() /vagrant/libs/doctrine2/vendor/phpunit/phpunit/src/TextUI/Command.php:123
PHP   5. PHPUnit_Runner_BaseTestRunner->loadSuiteClass() /vagrant/libs/doctrine2/vendor/phpunit/phpunit/src/Runner/BaseTestRunner.php:67
PHP   6. PHPUnit_Runner_StandardTestSuiteLoader->load() /vagrant/libs/doctrine2/vendor/phpunit/phpunit/src/Runner/BaseTestRunner.php:123
PHP   7. PHPUnit_Util_Fileloader::checkAndLoad() /vagrant/libs/doctrine2/vendor/phpunit/phpunit/src/Runner/StandardTestSuiteLoader.php:39
PHP   8. PHPUnit_Util_Fileloader::load() /vagrant/libs/doctrine2/vendor/phpunit/phpunit/src/Util/Fileloader.php:38

[Ocramius]

I'd say "go on and make a PR". Dropping 5.4 was indeed gonna happen :-)

[Ocramius]

Handled via #5863