Travis login command is silent when you specify an invalid github token

Re-posting closed issue here, so that it has a chance of being fixed in the product and saving future users some hassle.

Steps to reproduce:

$ travis login --github-token pancakes

Expected results:
A login failure message should be printed to the console.

Actual results:
Command exits and no output is printed to the console.

As a new user of travis, I erroneously assumed that a lack of output implied that the login command worked.