Travis has a feature to encrypt environment variables (“Encrypting environment variables”). This can be used to protect your secret API keys. I’ve successfully used this for my Heroku API key.
All you have to do is install the travis gem, encrypt the string you want and add the encrypted string in your .travis.yml. The encryption is only valid for one repository. The travis command gets your public key for your repo and can then decrypt the string during the build.
gem install --user travis
travis encrypt MY_SECRET_ENV=super_secret -r my_username/my_repo
This gives you the following output:
Please add the following to your .travis.yml file:
secure: "OrEeqU0z6GJdC6Sx/XI7AMiQ8NM9GwPpZkVDq6cBHcD6OlSppkSwm6JvopTR\newLDTdtbk/dxKurUzwTeRbplIEe9DiyVDCzEiJGfgfq7woh+GRo+q6+UIWLE\n3nowpI9AzXt7iBhoKhV9lJ1MROrnn4DnlKxAEUlHTDi4Wk8Ei/g="