Update readme and composer.json

I just went through and made the package name consistent for you. Before I list it in the main Omnipay repo, can you merge this pull request, and also rename the github repository to `lokielse/omnipay-alipay` (to make it consistent with the other omnipay gateways).

Then you will need to resubmit it to packagist.org with the new repository URL (just delete the current one).