Change phpunit/phpunit version

.travis.yml

@@ -40,9 +40,9 @@ before_install:
   - echo 'extension="memcache.so"' >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
   - echo 'extension="memcached.so"' >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
   - echo "extension=zmq.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
-  - yes | pecl install imagick
+  - yes | pecl install imagick-beta
 install:
-  - travis_retry composer install --optimize-autoloader --dev --prefer-source
+  - travis_retry composer require --dev phpunit/phpunit --sort-packages --optimize-autoloader --update-with-dependencies --prefer-source
   - travis_retry npm install
 before_script:
   - mysql -e 'CREATE DATABASE update39_test;CREATE DATABASE ab_test;CREATE DATABASE db_test;SET @@global.sql_mode=STRICT_ALL_TABLES;SET @@global.max_allowed_packet=33554432;SET @@global.wait_timeout=999999;'

composer.json

@@ -99,7 +99,6 @@
         "zend/gdata": "~1.12.1"
     },
     "require-dev":  {
-        "phpunit/phpunit": "~4.5",
         "mikey179/vfsStream": "~1.5"
     },
     "autoload":     {