For reference, this is the way I managed to setup TravisCI.org to automatically set the Heroku app on maintenance mode and capturing a backup before deploying to master (my production branch).

For reference, this is the way I managed to do it as of March 2016 starting with the link mentioned in this comment:

Added HEROKU_API_LOGIN (from heroku auth:whoami) and HEROKU_API_KEY (from heroku auth:token) as protected ENV variables in the travis.org build settings. Alternatively, they can be added in the .travis.yml with:
```
travis encrypt HEROKU_API_LOGIN ="$(heroku auth:whoami)" --add
travis encrypt HEROKU_API_KEY="$(heroku auth:token)" --add
```
Added following lines to the .travis.yml:
```
sudo: required
before_deploy:
  - ./.travis_before_deploy.sh
after_deploy:
  - ./.travis_after_deploy.sh
```
sudo: required is required since the use of container based build environments by default.

Created the file .travis_before_deploy.sh with the following content:

#!/bin/bash

set -e -o pipefail

if [ "${TRAVIS_BRANCH}" == "master" ]; then

  TARGET_APP_NAME="your_app_name"

  echo "Setting up '~/.ssh/config' to work with heroku."
  cat >> ~/.ssh/config <<EOF
Host heroku.com
   StrictHostKeyChecking no
   CheckHostIP no
   UserKnownHostsFile=/dev/null
EOF

  # DOC: https://devcenter.heroku.com/articles/authentication#usage-examples
  cat >> ~/.netrc <<EOF
machine api.heroku.com
  login ${HEROKU_API_LOGIN}
  password ${HEROKU_API_KEY}
EOF
  chmod 600 ~/.netrc

  echo "Installing heroku toolbelt"
  wget -qO- https://toolbelt.heroku.com/install-ubuntu.sh | sh

  echo "Setting maintenance mode 'on' on heroku's app"
  heroku maintenance:on --app "${TARGET_APP_NAME}"

  echo "Caturing DB backup from heroku's app"
  # DOC: https://devcenter.heroku.com/articles/heroku-postgres-backups#creating-a-backup
  heroku pg:backups capture --app "${TARGET_APP_NAME}"
fi

Created the file .travis_after_deploy.sh with the following content:

#!/bin/bash

set -e -o pipefail

if [ "${TRAVIS_BRANCH}" == "master" ]; then

  TARGET_APP_NAME="your_app_name"

  echo "Setting maintenance mode 'off' on heroku's app"
  heroku maintenance:off --app "${TARGET_APP_NAME}"

  echo "Application ready again. YAY!"
fi

rbf/automatic_heroku_maintenance_mode_from_travisci.md