Dropping support for older PHP versions (5.4, 5.5)

* Switched default ImageChartsQRCodeProvider to QRServerProvider

* Replace google image charts with image-charts.com

Merge branch 'master' of https://github.com/RobThree/TwoFactorAuth

* Fix a bug that caused timeslices to be returned instead of the inte…

…nded timeslice

* Upped version

Update README.md

* Updated composer.json

Update README.md

* Fix TwoFactorAuth class actually uses the TimeProvider

* Update README and DEMO to advise using 160+ bits secret

Update composer.json