Added tests for lowest versions of dependencies

.travis.yml

@@ -1,12 +1,24 @@
 language: php
 
-php:
-    - 5.3
-    - 5.4
-    - 5.5
+matrix:
+  include:
+    - php: 5.3
+      env: DEPENDENCIES='low'
+    - php: 5.3
+    - php: 5.4
+    - php: 5.5
+    - php: 5.6
+    - php: hhvm
+  allow_failures:
+    - env: DEPENDENCIES='low'
 
-before_script:
-    - curl -s http://getcomposer.org/installer | php
-    - php composer.phar --dev install
+before_install:
+  - composer self-update
 
-script: bin/phpunit --coverage-text
+install:
+  - export COMPOSER_ROOT_VERSION=dev-master
+  - if [ "$DEPENDENCIES" != "low" ]; then composer update; fi;
+  - if [ "$DEPENDENCIES" == "low" ]; then composer update --prefer-lowest; fi;
+
+script:
+  - ./bin/phpunit --testdox