Set up travis deployment

[hofbi]

Set up travis deployment to latex4ei without using ssh keypair.

Steps:

• Create new ssh key pair
• Add your private key an encryped environment-variable and put that during the build-process into a file and use it for authentification against the server.
• Add the public key to the server
• Add deploy step after_success to .travis.yml

Usefull Resources:

• https://docs.travis-ci.com/user/environment-variables/#Defining-Variables-in-Repository-Settings
• https://docs.travis-ci.com/user/encryption-keys