minor #10826 [2.3] Fix phpunit test suite on travis #2 (romainneutron)

This PR was merged into the 2.3 branch.

Discussion
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[2.3] Fix phpunit test suite on travis #2

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10821
| License       | MIT

This is a second approach to solve #10821.
Something is weird: `Symfony\Component\Form\Tests\Extension\Core\EventListener\TrimListenerTest` passes when using PHPUnit as phar and fails when using a composer global install

Commits
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32e5f67 [DependencyInjection] Fix travis unit tests
c7befd5 Update PHPUnit before run

.travis.yml

@@ -23,6 +23,7 @@ before_script:
     - sh -c 'if [ "$TRAVIS_PHP_VERSION" != "hhvm-nightly" ]; then echo "extension = memcache.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini; fi;'
     - sudo locale-gen fr_FR.UTF-8 && sudo update-locale
     - COMPOSER_ROOT_VERSION=dev-master composer --prefer-source --dev install
+    - wget https://phar.phpunit.de/phpunit.phar && rm `which phpunit` && sudo cp phpunit.phar /usr/local/bin/phpunit && sudo chmod +x /usr/local/bin/phpunit
 
 script:
     - ls -d src/Symfony/*/* | parallel --gnu --keep-order 'echo "Running {} tests"; phpunit --exclude-group tty,benchmark {};' || exit 1

src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/services8.xml

@@ -1,4 +1,4 @@
-<?xml version="1.0" ?>
+<?xml version="1.0" encoding="utf-8"?>
 
 <container xmlns="http://symfony.com/schema/dic/services"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"