Fix Repository::query docblock

Also remove unecessary instanciation with string.  This looked like a half completed idea.  See 14d9c9c
Remove useless code in Repository::findAll

The `or array()` does not assign an empty array to $files but boolean
false.  Anyway in case of error it's safe to use default instead of
silencing.
Use DIRECTORY_SEPARATOR instead of '/'
Query shall return Result not array
Commit composer.lock file

http://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file
Include HHVM to Travis tests