Fix figgyPudding error in npm token

It seems that a couple of lines were missed when token.js was [changed
to use figgyPudding][1] which [causes an error][2] when trying to run
that command in certain circumstances.  This patch fixes that error.

[1]: 4cf850d#diff-398ed3b014436a5204583323ea29320b
[2]: https://npm.community/t/npm-token-err-figgypudding-options-cannot-be-modified-use-concat-instead/10288

PR-URL: #259
Credit: @benblank
Close: #259
Reviewed-by: @isaacs

lib/token.js

@@ -118,7 +118,6 @@ function config () {
     })
   } else {
     conf = conf.concat({ auth: {} })
-    conf.auth = {}
   }
   if (conf.otp) conf.auth.otp = conf.otp
   return conf