merged branch igorw/travis (PR #576)

This PR was merged into the master branch.

Commits
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e58fa916 Test against PHP 5.5 on travis
d3f96597 Make travis install from source, fixes 403 responses

Discussion
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Travis: Fix 403 errors, test against PHP 5.5

.travis.yml

 language: php
 
-before_script: composer install --dev
+before_script: composer install --dev --prefer-source
 
 php:
   - 5.3
   - 5.4
+  - 5.5