Start an ssh-agent in travis

.travis.yml

@@ -23,6 +23,7 @@ after_success: |
   [ $TRAVIS_RUST_VERSION = nightly ] &&
   openssl aes-256-cbc -K $encrypted_9e86330b283d_key -iv $encrypted_9e86330b283d_iv -in .travis/deploy.enc -out .travis/deploy -d &&
   chmod 600 .travis/deploy &&
+  eval "$(ssh-agent -s)" &&
   ssh-add .travis/deploy &&
   pip install ghp-import --user $USER &&
   cp doc/index.html target/doc/ &&