Create a getter for TravisHelper's token

[jvcoutinho]

Problem
There's no way we can use TravisHelper to obtain the Travis' token. Combined with #71, this makes requesting things to Travis API impossible using the Mining Framework's utilities.

Cause
The token field is (correctly) private, but there's no getter for it.

Suggestion
Add a getter for the token field or add a method to make general requests to the Travis API.