ci: update travis config to use shared infra snippets

This commit changes the Travis configuration to use the shared infra
configuration to upload the build to GitHub pages. This has a few
advantages:

- The repository will benefit from improvements made to the shared
  configuration without needing any change.
- The history of the gh-pages branch will be overridden each build,
  reducing the clutter.

Author: pietroalbini

.travis.yml

@@ -1,29 +1,13 @@
 language: rust
-before_install:
-  - openssl aes-256-cbc -K $encrypted_1cc96cfefdcd_key -iv $encrypted_1cc96cfefdcd_iv -in rfcs-publish-key.enc -out ~/.ssh/rfcs-publish-key -d
-  - chmod u=rw,og= ~/.ssh/rfcs-publish-key
-  - echo "Host github.com" >> ~/.ssh/config
-  - echo "  IdentityFile ~/.ssh/rfcs-publish-key" >> ~/.ssh/config
-  - git --version
-script:
-  - rev=$(git rev-parse --short HEAD)
-  - (cargo install mdbook --vers '^0.2.0' --force || true)
-  - ./generate-book.sh
-  - cd book
-  - git init
-  - git config --global user.name "bors"
-  - git config --global user.email "bors@rust-lang.org"
-  - git remote add upstream git@github.com:rust-lang/rfcs.git
-  - git fetch upstream
-  - git reset upstream/gh-pages
-  - touch .
-  # We don't use jekyll. Disable it so it doesn't assign special meaning to any
-  # of our files (e.g. ignoring directories with a leading '_').
-  - touch .nojekyll
-  - git add -A .
-  - git commit -m "Rebuild book at ${rev}"
-  - git push -q upstream HEAD:gh-pages > /dev/null 2>&1
 branches:
   only:
     - master
 
+script:
+  - (cargo install mdbook --vers '^0.2.0' --force || true)
+  - ./generate-book.sh
+
+env:
+  RUSTINFRA_DEPLOY_DIR: book
+import:
+  - rust-lang/simpleinfra/travis-configs/static-websites.yml