Change Google+ mentions from the README.md to a Google service that still exists ;-)

[oliviermills]

For example:

https://github.com/googleapis/google-api-nodejs-client#generating-an-authentication-url
https://github.com/googleapis/google-api-nodejs-client#using-api-keys

[vijay-qlogic]

@JustinBeckwith Do we need to check all(around 153) repositories under googleapis?
I raised 2 PR:
#1458,
googleapis/google-api-php-client#1553

[JustinBeckwith]

Nah, I wouldn't go to all that trouble to be honest. In this case it's only funny because it's a sample we show directly on the README 🤦‍♂️ I mentioned this in the PR - but we should transition from the Google+ service over to Blogger.