add phpunit as dev requirement

.travis.yml

@@ -12,7 +12,11 @@ branches:
     - php5.2_backport
     - documentation
 services: redis-server
-script: phpunit -c phpunit.xml.travisci
+before_script:
+  - composer self-update
+  - composer install
+script:
+  - vendor/bin/phpunit -c phpunit.xml.travisci
 matrix:
   allow_failures:
     - php: hhvm

composer.json

@@ -15,6 +15,9 @@
     "require": {
         "php": ">=5.3.2"
     },
+    "require-dev": {
+        "phpunit/phpunit": "~3.7"
+    },
     "suggest": {
         "ext-phpiredis": "Allows faster serialization and deserialization of the Redis protocol",
         "ext-curl": "Allows access to Webdis when paired with phpiredis"