remove travis config file

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>

.travis.yml

-language: ruby
-sudo: false
-cache: bundler
-before_install:
- - sh ci/install_po4a.sh
-script:
- - bundle exec make all
-addons:
-  apt:
-    packages:
-      - libunicode-linebreak-perl
-      - python3-polib
-notifications:
-  email:
-    on_success: never
-    on_failure: always