Remove dev flag on composer install

It's deprecated and the default behavior is to install dev dependencies now.

Seriously this time! (traderinteractive#12)

* Update dependencies

* Remove support for PHP 5.6

Note: The application should still work on 5.6 tests are not executed
on that version anymore.

* Update composer lock

Merge pull request traderinteractive#6 from dominionenterprises/devel…

…opment

Update README.md

Merge pull request traderinteractive#4 from dominionenterprises/devel…

…opment

Add license to composer.json

Merge pull request traderinteractive#3 from dominionenterprises/devel…

…opment

traderinteractive#1

Fix tests and update usage.