Updating composer packages and travis configuration to ensure builds …

…for the current supported versions.

.travis.yml

@@ -1,15 +1,17 @@
 language: php
 
-dist: trusty
-
 php:
-  - 5.5
-  - 5.6
-  - 7.0
   - 7.1
   - 7.2
   - 7.3
-  - nightly
+
+matrix:
+  allow_failures:
+  - php: 5.3
+  - php: 5.4
+  - php: 5.5
+  - php: 5.6
+  - php: nightly
 
 sudo: false
 
@@ -18,5 +20,5 @@ install: travis_retry composer install --no-interaction --prefer-source --dev
 script: vendor/bin/phpunit --coverage-clover=coverage.clover
 
 after_script:
-    - wget https://scrutinizer-ci.com/ocular.phar
-    - php ocular.phar code-coverage:upload --format=php-clover coverage.clover
+  - wget https://scrutinizer-ci.com/ocular.phar
+  - php ocular.phar code-coverage:upload --format=php-clover coverage.clover