doc/travis_ci: remove future enhancements" section

It is no longer relevant, since we no longer publish .deb packages.

Author: borsboom

doc/travis_ci.md

@@ -178,14 +178,3 @@ install:
 - [simonmichael/hledger](https://github.com/simonmichael/hledger/blob/master/.travis.yml)
 - [fpco/wai-middleware-crowd](https://github.com/fpco/wai-middleware-crowd/blob/master/.travis.yml)
 - [commercialhaskell/all-cabal-hashes-tool](https://github.com/commercialhaskell/all-cabal-hashes-tool/blob/master/.travis.yml)
-
-## Future enhancements
-
-Once Travis whitelists the stack .deb files, we'll be able to simply include
-stack in the `addons` section, and automatically use the newest version of
-stack, avoiding that complicated `before_install` section This is being
-tracked in the
-[apt-source-whitelist](https://github.com/travis-ci/apt-source-whitelist/pull/7)
-and
-[apt-package-whitelist](https://github.com/travis-ci/apt-package-whitelist/issues/379)
-issue trackers.