PHP 5.5 support

[wimulkeman]

Does the App Search client have parts which makes it unusable for PHP 5.5? If not, would it be possible to add PHP 5.5 support to composer?

The reason for this request is that Ubuntu servers which still run PHP 5 often supports PHP 5.5.9, but not PHP 5.6 while connecting to App Search through this package can still come in handy.

I could create a pull request if this request is supported.