Fix broken build

    - `gem install` no longer recognizes the `--no-ri` and `--no-rdoc` options. Use `--no-document` instead.
    - References:
        - rubygems/rubygems#2354
        - rubygems/bundler#6624

.travis.yml

@@ -44,7 +44,7 @@ after_success:
   - goveralls -service=travis-ci -coverprofile /tmp/coverage/combined.txt
   - make list-external-deps > dependency_tree.txt && cat dependency_tree.txt
   - make build-cli
-  - gem install --no-ri --no-rdoc fpm 
+  - gem install --no-document fpm
   - fpm -s dir -t deb -n migrate -v "$(git describe --tags 2>/dev/null | cut -c 2-)" --license MIT -m [email protected] --url https://github.com/golang-migrate/migrate --description='Database migrations' -a amd64 -p migrate.$(git describe --tags 2>/dev/null | cut -c 2-).deb --deb-no-default-config-files -f -C cli/build migrate.linux-amd64=/usr/local/bin/migrate
 
 deploy:
@@ -124,6 +124,7 @@ deploy:
       tags: true
   - provider: script
     script: ./docker-deploy.sh
+    skip_cleanup: true
     on:
       go: "1.11.x"
       repo: golang-migrate/migrate