Simplified the Travis configuration

The Mongo extension is already available so we can enable it without using pecl. There is no need to support testing several versions of the driver.
This also uses the global composer setup available on Travis and adds PHP 5.6 testting

Author: stof

.travis.yml

@@ -4,13 +4,10 @@ php:
   - 5.3
   - 5.4
   - 5.5
-
-env:
-  - MONGO_VERSION=1.3.7
+  - 5.6
 
 before_script:
-  - pecl -q install -f mongo-${MONGO_VERSION} && echo "extension=mongo.so" >> `php --ini | grep "Loaded Configuration" | sed -e "s|.*:\s*||"`
-  - curl -s http://getcomposer.org/installer | php
-  - php composer.phar install --dev --prefer-dist --no-interaction
+  - echo "extension=mongo.so" >> `php --ini | grep "Loaded Configuration" | sed -e "s|.*:\s*||"`
+  - composer install --dev --prefer-dist --no-interaction
 
 phpunit: phpunit --coverage-text