Attempting to fix phpunit version conflict in TravisCI

.travis.yml

@@ -3,13 +3,6 @@ php:
   - 5.5
   - 5.6
   - 7.0
-matrix:
-  fast_finish: true
-  include:
-    - php: 5.5
-      env: deps="low"
 before_script:
-  - if [ "$PHPUNIT_VERSION" != "" ]; then composer require --no-update "phpunit/phpunit:${PHPUNIT_VERSION}"; fi
-  - if [ "$deps" = "low" ]; then composer update --prefer-lowest; fi
-  - if [ "$deps" = "" ]; then composer install; fi
+  - composer install
 script: vendor/bin/phpunit