Fixed returned toString encoding of OAuth2Client.prototype.decodeBase64 method.
Fixed returned toString encoding of OAuth2Client.prototype.decodeBase64 method.

murgatroid99/google-auth-library-nodejs,tbetbetbe/google-auth-library-nodejs,JustinBeckwith/google-auth-library-nodejs,mlmorg/google-auth-library-nodejs,googleapis/google-auth-library-nodejs,JustinBeckwith/google-auth-library-nodejs,googleapis/google-auth-library-nodejs,JustinBeckwith/google-auth-library-nodejs,JustinBeckwith/google-auth-library-nodejs