Updates minimum versions of OAuth deps

[kennethormandy]

This Pull Request makes it possible to install the plugin alongside other plugins using more recent versions of the Google or GitHub OAuth plugins.This issue originally came up here: https://github.com/kennethormandy/craft-marketplace/issues/20

From the changelogs, it didn’t appear that this would have API changes that would impact this plugin, but I am not 100% sure about that.

• thephpleague/oauth2-google changelog
• thephpleague/oauth2-github changelog

For the Google plugin, it might be fine to add v4.x to the allowed range too.

Thanks!

[Mosnar]

Thanks!