Enable ssh with public key authentication

.travis.yml

@@ -2,6 +2,11 @@
 # see http://sachachua.com/blog/2015/02/continuous-integration-code-coverage-emacs-packages-travis-coveralls/
 language: emacs-lisp
 before_install:
+  # enable ssh
+  - sed -i 's/.*PubkeyAuthentication.*/PubkeyAuthentication yes/'
+  - service ssh restart
+  - ssh-keygen -t rsa -C "<me@mymail>" -f ~/.ssh/id_this_travis_build
+  - cat ~/.ssh/id_this_travis_build.pub >> ~/.ssh/authorized_keys
   # PPA for Emacs nightlies
   - sudo add-apt-repository -y ppa:ubuntu-elisp/ppa
   # Update and install the Emacs for our environment