Add NVM_AUTO_REVERT option when using NVM_AUTO_USE

[lucraraujo]

I created an option to disable the "auto revert" feature. I find the "auto use" a little bit annoying due to auto revert. It may slow down my terminal use because every time a leave a folder with a .nvmrc file, it will revert to default nvm environment configured. I need some help to write the tests since I'm not used to the test tool used in the project.

[lukechilds]

Thanks, this looks like a good change 👍

I have limited time to spend on OSS at the moment but I'll give you a hand with the tests when I can.

Feel free to give it a bash on your own if you feel up to it.